Methods for targeted in vitro and in vivo drug delivery to mammalian cells via bacterially derived intact minicells

ABSTRACT

A composition comprising intact minicells that contain a drug molecule is useful for targeted drug delivery. One targeted drug delivery method employs bispecific ligands, comprising a first arm that carries specificity for a bacterially derived minicell surface structure and a second arm that carries specificity for a mammalian cell surface receptor, to target drug-loaded minicells to specific mammalian cells and to cause endocytosis of the minicells by the mammalian cells. Another drug delivery method exploits the natural ability of phagocytic mammalian cells to engulf minicells without the use of bispecific ligands.

BACKGROUND OF THE INVENTION

The present invention relates to ongoing efforts to achieve controlleddrug release and drug targeting to specific tissues, particularly in thearea of cancer chemotherapy. More particularly, the invention relates totargeted drug delivery by means of intact bacterial minicells, which areable to deliver drugs intracellularly, within desired target cellsin-vivo and in-vitro. Minicells containing chemical or biochemical drugsconstitute novel delivery vehicles, capable of being targeted tospecific cells. One method of targeting these vehicles employsbispecific molecules that specifically bind to both a minicell surfacestructure and a target cell surface structure, such as a receptor. Thebispecific ligands mediate an interaction between the minicells andtarget cells, such that the target cells engulf the minicells, whichrelease their drug payload into the cytoplasm of the target cells. Oncecytoplasmically released, the drug acts on intracellular targets, suchas intracellular organelles, the nucleus, the cytoskeleton, enzymes, andco-factors, to achieve a therapeutic effect. In another method of drugdelivery, phagocytosis- or endocytosis-competent target cells engulfdrug-loaded minicells without the use of bispecific ligands.

Currently, most drugs used for treating cancer are administeredsystemically. Although systemic delivery of cytotoxic anticancer drugsplays a crucial role in cancer therapeutics, it also engenders seriousproblems. For instance, systemic exposure of normal tissues/organs tothe administered drug can cause severe toxicity (Sarosy and Reed, 1993).This is exacerbated by the fact that systemically delivered cancerchemotherapy drugs often must be delivered at very high dosages toovercome poor bioavailability of the drugs and the large volume ofdistribution within a patient. Also, systemic drug administration can beinvasive, as it often requires the use of a secured catheter in a majorblood vessel. Because systemic drug administration often requires theuse of veins, either peripheral or central, it can cause localcomplications such as phlebitis. Extravasation of a drug also can leadto vesicant/tissue damage at the local site of administration, such asis commonly seen upon administration of vinca alkaloids andanthracyclines.

Because existing systems for targeted drug delivery are seriouslydeficient, current cancer drug treatment strategies poorly address theproblems that attend systemic drug administration. One approach foraddressing these problems involves simply modifying administrationschedules or infusion regimens, which may be either bolus, intermittent,or continuous. This approach, however, provides very limited benefits.

Some alternative approaches to intravenous injection also exist, eachdesigned to provide regional delivery, i.e., selective delivery to atumor region. Examples of such alternatives include polymeric implants,intra-peritoneal infusion, intra-pleural infusion, intra-arterialdelivery, chemo-embolization, and inhalation of aerosols. In particular,intra-peritoneal administration of chemotherapy has been studiedextensively for ovarian carcinoma and other abdominal tumors (Kirmani etal., 1994; Alberts et al., 1996). Unfortunately, each of these deliverymethods, including intra-peritoneal administration, has achieved onlymarginal success at selectively delivering drugs to a tumor site andreducing side effects.

Other attempts to address the problems with systemic delivery ofcytotoxic anticancer drugs include the use of alternative drugformulations and delivery systems, including controlled-releasebiodegradable polymers, polymeric microsphere carriers and liposomes, aswell as the co-administration of cytoprotective agents withantineoplastics. Chonn and Cullis, 1995; Kemp et al., 1996; Kumanohosoet al., 1997; Schiller et al., 1996; Sharma et al., 1996; Sipos et al.,1997.

The use of liposomes as drug carriers for chemotherapeutic agentsoriginally was proposed as a means for manipulating drug distribution toimprove anti-tumor efficacy and to reduce toxicity (reviewed by Allen,1997). Through encapsulation of drugs in a macromolecular carrier, suchas a liposome, the volume of distribution is significantly reduced andthe concentration of drug in a tumor is increased. This causes adecrease in the amounts and types of nonspecific toxicities, and anincrease in the amount of drug that can be effectively delivered to atumor (Papahadjopoulos and Gabizon, 1995; Gabizon and Martin, 1997;Martin, 1998). Liposomes protect drugs from metabolism and inactivationin plasma. Further, due to size limitations in the transport of largemolecules or carriers across healthy endothelia, drugs accumulate to areduced extent in healthy tissues (Mayer et al., 1989; Working et al.,1994).

To prolong their circulation time, liposomes are coated withpolyethylene glycol (PEG), a synthetic hydrophilic polymer (Woodle andLasic, 1992). The PEG headgroup serves as a barrier, stericallyinhibiting hydrophobic and electrostatic interactions with a variety ofblood components and plasma opsonins at the liposome surface, andthereby retards recognition of liposomes by the reticuloendothelialsystem. PEG-coated liposomes are termed “sterically stabilized” (SSL) orSTEALTH liposomes (Lasic and Martin, 1995). This technology gave rise toa commercial pharmaceutical formulation of pegylated liposomalDoxorubicin, known as Doxil in the U.S. and Caelyx in Europe. A widearray of other drugs also have been encapsulated in liposomes for cancertreatment (Heath et al., 1983; Papahadjopoulos et al., 1991; Allen etal., 1992; Vaage et al., 1993b; Burke and Gao, 1994; Sharma et al.,1995; Jones et al., 1997; Working, 1998).

Liposomal drug carriers, unfortunately, have several drawbacks. Forexample, in vivo, drugs often leak out of liposomes at a sufficient rateto become bioavailable, causing toxicity to normal tissues. Similarly,liposomes are unstable in vivo, where their breakdown releases drug andcauses toxicity to normal tissues. Also, liposomal formulations ofhighly hydrophilic drugs can have prohibitively low bioavailability at atumor site, because hydrophilic drugs have extremely low membranepermeability. This limits drug release once liposomal carriers reach atumor. Highly hydrophobic drugs also tend to associate mainly with thebilayer compartment of liposomes, causing low entrapment stability dueto rapid redistribution of a drug to plasma components. Additionally,some drugs, such as 1-β-D-arabinofuranosylcytosine (ara-C) andmethotrexate, only enter tumor cells directly, via membrane transporters(Plageman et al., 1978; Wiley et al., 1982; Westerhof et al., 1991,1995; Antony, 1992). In such cases, a liposomal carrier would need torelease sufficient drug near a tumor site to achieve a therapeuticeffect (Heath et al., 1983; Matthay et al., 1989; Allen et al., 1992).Lastly, the use of conventional liposome formulations increases apatient's risk of acquiring opportunistic infections (White, 1997),owing to localization of drugs in reticuloendothelial system macrophagesand an attendant macrophage toxicity (Allen et al., 1984; Daemen et al.,1995, 1997). This problem becomes accentuated in immune deficientpatients, such as AIDS patients being treated for Kaposi's sarcoma.

Because problems continue to hamper significantly the success of cancertherapeutics, an urgent need exists for targeted drug deliverystrategies that will either selectively deliver drugs to tumor cells andtarget organs, or protect normal tissues from administeredantineoplastic agents. Such strategies should improve the efficacy ofdrug treatment by increasing the therapeutic indexes of anticanceragents, while minimizing the risks of drug-related toxicity.

An international patent application, PCT/IB02/04632, has describedrecombinant, intact minicells that contain therapeutic nucleic acidmolecules. Such minicells are effective vectors for deliveringoligonucleotides and polynucleotides to host cells in vitro and in vivo.Data presented in PCT/IB02/04632 demonstrated, for example, thatrecombinant minicells carrying mammalian gene expression plasmids can bedelivered to phagocytic cells and to non-phagocytic cells. Theapplication also described the genetic transformation ofminicell-producing parent bacterial strains with heterologous nucleicacids carried on episomally-replicating plasmid DNAs. Upon separation ofparent bacteria and minicells, some of the episomal DNA segregated intothe minicells. The resulting recombinant minicells were readily engulfedby mammalian phagocytic cells and became degraded within intracellularphagolysosomes. Surprisingly, some of the recombinant DNA escaped thephagolysosomal membrane and was transported to the mammalian cellnucleus, where the recombinant genes were expressed. Thus, theapplication showed a usefulness for minicells in human and animal genetherapy.

The present invention builds on these recent discoveries relating tominicells, and addresses the continuing needs for improved drug deliverystrategies, especially in the context of cancer chemotherapy.

SUMMARY OF THE INVENTION

To address these and other needs, the present invention provides, in oneaspect, a composition consisting essentially of intact minicells thatcontain a drug, such as a cancer chemotherapy drug. In a related aspect,the invention provides a composition comprising (i) bacterially derivedintact minicells and (ii) a pharmaceutically acceptable carriertherefor, where the minicells contain a drug.

According to another aspect, the invention provides a targeted drugdelivery method that comprises bringing bispecific ligands into contactwith (i) bacterially derived minicells that contain a desired drug and(ii) mammalian cells, preferably non-phagocytic mammalian cells. Thebispecific ligands have specificity for both a surface component on theminicells and a surface component on the mammalian cells. As a result,the ligands cause the minicells to bind to the mammalian cells, theminicells are engulfed by the mammalian cells, and the drug is releasedinto the cytoplasm of the mammalian cells.

The invention also provides bispecific ligands useful for targetingminicell vehicles to mammalian host cells. The bispecific ligand may bepolypeptide, carbohydrate or glycopeptide; and may comprise an antibodyor antibody fragment. In preferred embodiments, the bispecific ligandhas a first arm that carries specificity for a bacterial minicellsurface structure and a second arm that carries specificity for amammalian cell surface structure. A desirable minicell surface structurefor ligand binding is an O-polysaccharide component of alipopolysaccharide. Desirable mammalian cell surface structures forligand binding are receptors, preferably those capable of activatingreceptor-mediated endocytosis.

In another aspect, the invention provides a composition comprising (i) abacterially derived minicell that contains a drug molecule and (ii) abispecific ligand that is capable of binding to a surface component ofthe minicell and to a surface component of a mammalian cell.

The invention provides another drug delivery method that entailsbringing bacterially derived minicells that contain a drug into contactwith target mammalian cells that are phagocytosis- orendocytosis-competent. The mammalian cells engulf the drug-loadedminicells, which then release their drug payload intracellularly.

The invention further provides methodology for loading minicells with adrug. One such method involves creating a concentration gradient of thedrug between an extracellular medium containing the minicells and theminicell cytoplasm. The drug naturally moves down this concentrationgradient, into the minicell cytoplasm.

Another method of loading minicells with a drug involves culturing arecombinant parent bacterial cell under conditions wherein the parentbacterial cell transcribes and translates a therapeutic nucleic acidencoding the drug, such that the drug is released into the cytoplasm ofthe parent bacterial cell. When the parent bacterial cell divides andforms progeny minicells, the minicells also contain the drug in theircytoplasm.

Yet another method of loading minicells with a drug involves culturing arecombinant minicell that contains a therapeutic nucleic acid encodingthe drug under conditions such that the therapeutic nucleic acid istranscribed and translated within the minicell.

The invention also provides for the use of bacterially derived intactminicells and bispecific ligands in preparing a medicament for use in amethod of treating disease or modifying a trait by administration of themedicament to a cell, tissue or organ. In the medicament, minicellscontain a drug molecule and bispecific ligands that are capable ofbinding to the minicells and to target mammalian cells. Such medicamentsare useful to treat various conditions and diseases, including acquireddiseases such as AIDS, pneumonia and tuberculosis, but are particularlyuseful in the context of cancer chemotherapy.

The invention affords significant improvements over conventional drugtherapy techniques by (i) reducing drug-related toxicity, because thedrug is specifically delivered intracellularly within target cells, (ii)alleviating drug-associated side effects at the site of administrationin a human or animal, because the drug is packaged within minicells andnot free to interact with non-targeted cells and tissues at the site ofadministration, (iii) eliminating the need for continuous infusion ofdrug, because a therapeutic dose of targeted and drug-packaged minicellscan be administered by routine injection, (iv) reducing the effectivedose of a drug, because specific targeting is achieved, and (v)sometimes eliminating the need to purify the drug, because the drug canbe synthesized biologically by either the minicell drug delivery vehicleor the parent bacteria. The use of minicells for both drug biosynthesisand targeted delivery to desired mammalian cells constitutes aparticular advantage, because many drugs conventionally are extractedfrom rare plant or marine sources, or are very difficult to synthesizechemically. Additionally, some chemotherapeutic drugs, includingmethotrexate, gain entry into mammalian cells via a membrane-associatedactive transport mechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a chart showing high performance liquid chromatography (HPLC)and liquid chromatograph-mass spectrometry (LC-MS) quantitation ofDoxorubicin packaged in minicells (minicells_(DOX)). 5×10⁸ minicellswere packaged with various concentrations of Doxorubicin in the externalmedium (shown on the x-axis). The minicells_(DOX) were purified and theDoxorubicin was extracted using novel procedures (described in Example3). Doxorubicin concentration in the extracts was measured using HPLC(circles) and LC-MS (triangles) and plotted on the y-axis.

FIG. 2 is a chart showing drug delivery via minicells_(DOX) to humanbreast adenocarcinoma cells (MDA-MB-468) in-vitro. A cell cytotoxicityassay was performed on cells treated with EGFR-targeted minicells_(DOX)(^(EGFR)minicells_(DOX)), non-targeted minicells_(DOX)(^(non-targeted)minicells_(DOX)), free Doxorubicin and untreated cells.Within 6 days after treatment, cells treated with either freeDoxorubicin or ^(EGFR)minicells_(DOX) exhibited only about 30%viability. Untreated cells and cells treated with^(non-targeted)minicells_(DOX) showed normal cell viability.

FIG. 3 is a chart showing a highly significant therapeutic effect ofEGFR-targeted, Doxorubicin-packaged minicells (^(EGFR)minicells_(DOX))on human breast cancer xenografts. Tumor volume is shown on the y-axis,and days post-xenograft establishment are shown on the x-axis. Solidtriangles below the x-axis indicate the days on which various treatmentswere administered. Open triangles below the x-axis indicate a change inthe treatment of control groups G5 and G6, where ^(EGFR)minicells_(DOX)were administered instead of ^(non-targeted)minicells_(DOX). The legendidentifies the various treatments administered to each of 8 groups ofmice (n=11 per group).

FIG. 4 is a chart showing a highly significant therapeutic effect ofEGFR-targeted, Paclitaxel-packaged minicells (^(EGFR)minicells_(Pac)) onhuman breast cancer xenografts. Tumor volume is shown on the y-axis, anddays post-xenograft establishment are shown on the x-axis. Solidtriangles below the x-axis indicate the days on which various treatmentswere administered. The legend identifies the various treatmentsadministered to each of 8 groups of mice (n=11 per group).

FIG. 5 is a chart showing a highly significant therapeutic effect ofHER2/neu-targeted, Doxorubicin-packaged minicells(^(HER2)minicells_(DOX)) on human ovarian cancer xenografts. Theminicells were derived from S. Typhimurium (S.t.) or E. coli (E.c.)minCDE-parent strains. Tumor volume is shown on the y-axis, and dayspost-xenograft establishment are shown on the x-axis. Solid trianglesbelow the x-axis indicate the days on which various treatments wereadministered. The legend identifies the various treatments administeredto each of 7 groups of mice (n=11 per group).

FIG. 6 is a chart showing a dose-response effect on tumorstabilization/regression by EGFR-targeted, Doxorubicin-packagedminicells (^(EGFR)minicells_(DOX)). MDA-MB-468 tumor xenografts wereestablished in Balb/c nu/nu mice, and groups (n=11) were treatedintravenously with 10⁶, 10⁷ or 10^(8 EGFR)minicells_(DOX) containing twodifferent concentrations of Doxorubicin. Tumor volume is shown on they-axis, and days post-xenograft establishment are shown on the x-axis.Solid triangles below the x-axis indicate the days on which varioustreatments were administered. The legend identifies the varioustreatments administered to each of 7 groups of mice.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have determined that bacterially derived intactminicells are effective vehicles for packaging and delivering drugs totarget mammalian cells in vitro and in vivo. More particularly, theinventors have found that a minicell carrying a drug payload can bedirected to target cells, which internalize the minicell and process itsuch that the drug payload is released into the cytoplasm of the targetcell. Surprisingly, the drug survives this process without becomingdegraded.

In one example of these discoveries, the inventors observed thatdrug-packaged minicells can be targeted to cancer cells, internalizedinto the cancer cells in vitro, and degraded within late endosomes orphagolysosomes, thereby releasing therapeutically effective amounts ofbioactive drug into the cancer cell cytoplasm. See the examples, below.

In a further example, these observations were corroborated by in-vivostudies using human tumor xenografts in nude mice. Intravenous deliveryof drug-packaged minicells demonstrated highly significant tumorxenograft reduction in all mice (11 mice per group). See the examples,below.

Thus, the inventors have discovered (i) that a range of different drugscan be packaged into intact minicells, (ii) that drugs move one-way fromthe extracellular environment into the cytoplasm of intact minicells,(iii) that therapeutically significant concentrations of drugs can betransferred into the cytoplasm of intact minicells, (iv) that intactminicell membranes are impervious to drug leakage from minicellcytoplasm, (v) that attachment of bispecific ligands to surfacestructures of drug-packaged minicells does not destabilize the minicellsand that minicells can thereby specifically bind to target mammaliancells both in-vitro and in-vivo, (vi) that phagocytosis- orendocytosis-competent mammalian cells engulf drug-packaged minicells,(vii) that non-phagocytic mammalian cells rapidly engulf surfacereceptor-bound drug-packaged minicells, (viii) that after engulfedminicells are degraded within vacuoles, significant amounts of bioactivedrug escape the vacuolar membrane, (viii) that the escaped drug canaffect its intracellular target within the mammalian cell, (ix) thatchemotherapeutic drug-packaged minicells can permeate leaky vasculaturesurrounding tumor masses in vivo, (x) that highly significanttherapeutic effects, including tumor regression and diseasestabilization, can be achieved using chemotherapeutic drug-packagedminicells, and (xi) that drug-packaged minicells significantly reduce oreliminate unwanted toxicity.

The ability of minicells to package drugs is surprising for severalreasons. It is surprising that that intact minicell membranes arepermeable to a range of structurally dissimilar hydrophilic, hydrophobicand amphipatic drugs. By contrast, live bacterial cells exhibitselective membrane permeability to solutes, so it appears that minicellshave lost this selectivity. It also is surprising that minicells areunable to expel drugs from their cytoplasm, because live bacterial cellsextrude noxious chemicals that enter into the bacterial cytoplasm. Evenagainst a reverse osmotic gradient, in which drug-loaded minicells aresuspended in phosphate-buffered saline containing no drug, minicellsretain drug. This is additionally surprising because drugs appear simplyto diffuse into minicells through intact minicell membranes, yet thediffusion channels are not available for drugs to diffuse out ofminicells. Another unexpected aspect of the present invention is thattherapeutically significant drug concentrations can be packaged withinminicells, because bacterial cytoplasm (and, hence, minicell cytoplasm)contains significant concentrations of biocompatible solutes. Thus, itwas believed that there might be insufficient spare intracellular spaceto accommodate high concentrations of non-biocompatible drug solutes,without loss of minicell integrity.

The ability of minicells to deliver drugs also is surprising for severalreasons. It is unexpected, for example, that drug-packaged minicells donot leak drug into the extracellular space. This is a persistent problemwith liposomal drug delivery vectors, and minicells, like liposomes, arenon-living vesicles. Nevertheless, although intact minicell membraneslack selectivity to drug permeation, the membrane integrity issufficient to prevent leakage of intracellular solutes. Also surprising,and unlike liposomal drug delivery vectors, attachment of ligands to thesurface of drug-packaged minicells does not cause destabilization ofminicell integrity or membrane perturbations that result in drugleakage. Further, it is unexpected that drug-packaged minicells areendocytosed rapidly by non-phagocytic mammalian cells, simply by virtueof a bispecific ligand linking the two. It was widely believedheretofore that large particles, like bacteria, can only penetrate andinvade non-phagocytic mammalian cells via an active process involvingsecretion of invasion-associated proteins by a live pathogen. Minicellsare non-living vesicles lacking the ability to actively invadenon-phagocytic mammalian cells. Yet another surprise was thatdrug-packaged minicells carrying a bispecific ligand are able toextravasate tumor neovasculature in vivo. While there is considerabledebate regarding the leakiness of tumor mincroenvironmentneovasculature, the current view is that pores in the neovasculature are150-400 nm in diameter (Gabizon et al., 2003). Minicells carrying asurface ligand, however, are 400 nm to 600 nm in diameter, yet still areable to extravasate tumor neovasculature in-vivo. The ability of drugspackaged in minicells to avoid degradation also is surprising forseveral reasons. Engulfed minicells are subjected to lysosomal andlate-endosomal environments known to be harsh, and which break downminicells. Despite the harshness of these environments, the inventorsobserved that a range of drugs are released from minicells in abiologically active form and remain significantly unaltered. Perhapseven more surprising was the discovery that a significant concentrationof drug is able to escape, in its active form, into the mammalian cellcytoplasm. Pursuant to the present invention, that is, drugconcentrations within mammalian cells are sufficient to work atherapeutic effect in both in vitro and in vivo experiments.

Yet another surprising discovery is that drug-packaged minicellsminimize adverse side effects. For example, at the site of intravenousinjection in the tail vein of nude mice, free drug injections causesevere skin reactions, whereas drug-packaged minicells do not cause suchan adverse side effect.

In accord with these discoveries, the invention provides a compositionconsisting essentially of intact minicells that contain a desired drug,such as a cancer chemotherapy drug. The invention also provides acomposition comprising (i) bacterially derived intact minicells and (ii)a pharmaceutically acceptable carrier therefor, where the minicellscontain a drug, such as a cancer chemotherapy drug.

Minicells of the invention are anucleate forms of E. coli or otherbacterial cells, engendered by a disturbance in the coordination, duringbinary fission, of cell division with DNA segregation. Prokaryoticchromosomal replication is linked to normal binary fission, whichinvolves mid-cell septum formation. In E. coli, for example, mutation ofmin genes, such as minCD, can remove the inhibition of septum formationat the cell poles during cell division, resulting in production of anormal daughter cell and an anucleate minicell. See de Boer et al.,1992; Raskin & de Boer, 1999; Hu & Lutkenhaus, 1999; Harry, 2001.Minicells are distinct from other small vesicles that are generated andreleased spontaneously in certain situations and, in contrast tominicells, are not due to specific genetic rearrangements or episomalgene expression. For practicing the present invention, it is desirablefor minicells to have intact cell walls (“intact minicells”).

In addition to min operon mutations, anucleate minicells also aregenerated following a range of other genetic rearrangements or mutationsthat affect septum formation, for example in the divIVB1 in B. subtilis.See Reeve and Cornett, 1975; Levin et al., 1992. Minicells also can beformed following a perturbation in the levels of gene expression ofproteins involved in cell division/chromosome segregation. For example,overexpression of minE leads to polar division and production ofminicells. Similarly, chromosome-less minicells may result from defectsin chromosome segregation for example the smc mutation in Bacillussubtilis (Britton et al., 1998), spoOJ deletion in B. subtilis (Iretonet al., 1994), mukB mutation in E. coli (Hiraga et al., 1989), and parCmutation in E. coli (Stewart and D'Ari, 1992). Gene products may besupplied in trans. When over-expressed from a high-copy number plasmid,for example, CafA may enhance the rate of cell division and/or inhibitchromosome partitioning after replication (Okada et al., 1994),resulting in formation of chained cells and anucleate minicells (Wachiet al., 1989; Okada et al., 1993). Minicells can be prepared from anybacterial cell of Gram-positive or Gram-negative origin.

Minicells of the invention contain one or more drugs. The term “drug”includes any physiologically or pharmacologically active substance thatproduces a local or systemic effect in animals, particularly mammals andhumans. Drugs may be inorganic or organic compounds, without limitation,including peptides, proteins, nucleic acids, and small molecules, any ofwhich may be characterized or uncharacterized. They may be in variousforms, such as unchanged molecules, molecular complexes,pharmacologically acceptable salts, such as hydrochloride, hydrobromide,sulfate, laurate, palmitate, phosphate, nitrite, nitrate, borate,acetate, maleate, tartrate, oleate, salicylate, and the like. For acidicdrugs, salts of metals, amines or organic cations, for example,quaternary ammonium, can be used. Derivatives of drugs, such as bases,esters and amides also can be used. A drug that is water insoluble canbe used in a form that is a water soluble derivative thereof, or as abase derivative thereof, which in either instance, or by its delivery,is converted by enzymes, hydrolyzed by the body pH, or by othermetabolic processes to the original therapeutically active form.

Drugs having any physiological or pharmacological activity are useful inthis invention, but cancer chemotherapy agents are preferred drugs.Useful cancer chemotherapy drugs include nitrogen mustards,nitrosorueas, ethyleneimine, alkane sulfonates, tetrazine, platinumcompounds, pyrimidine analogs, purine analogs, antimetabolites, folateanalogs, anthracyclines, taxanes, vinca alkaloids, topoisomeraseinhibitors and hormonal agents. Exemplary chemotherapy drugs areActinomycin-D, Alkeran, Ara-C, Anastrozole, Asparaginase, BiCNU,Bicalutamide, Bleomycin, Busulfan, Capecitabine, Carboplatin,Carboplatinum, Carmustine, CCNU, Chlorambucil, Cisplatin, Cladribine,CPT-11, Cyclophosphamide, Cytarabine, Cytosine arabinoside, Cytoxan,Dacarbazine, Dactinomycin, Daunorubicin, Dexrazoxane, Docetaxel,Doxorubicin, DTIC, Epirubicin, Ethyleneimine, Etoposide, Floxuridine,Fludarabine, Fluorouracil, Flutamide, Fotemustine, Gemcitabine,Herceptin, Hexamethylamine, Hydroxyurea, Idarubicin, Ifosfamide,Irinotecan, Lomustine, Mechlorethamine, Melphalan, Mercaptopurine,Methotrexate, Mitomycin, Mitotane, Mitoxantrone, Oxaliplatin,Paclitaxel, Pamidronate, Pentostatin, Plicamycin, Procarbazine,Rituximab, Steroids, Streptozocin, STI-571, Streptozocin, Tamoxifen,Temozolomide, Teniposide, Tetrazine, Thioguanine, Thiotepa, Tomudex,Topotecan, Treosulphan, Trimetrexate, Vinblastine, Vincristine,Vindesine, Vinorelbine, VP-16, and Xeloda.

Minicell-containing compositions of this invention preferably containfewer than about 1 contaminating parent bacterial cell per 10⁷minicells, more preferably contain fewer than about 1 contaminatingparent bacterial cell per 10⁸ minicells, even more preferably containfewer than about 1 contaminating parent bacterial cell per 10⁹minicells, still more preferably contain fewer than about 1contaminating parent bacterial cell per 10¹⁰ minicells and mostpreferably contain fewer than about 1 contaminating parent bacterialcell per 10¹¹ minicells.

Methods of purifying minicells are known in the art and described inPCT/IB02/04632. One such method combines cross-flow filtration (feedflow is parallel to a membrane surface; Forbes, 1987) and dead-endfiltration (feed flow is perpendicular to the membrane surface).Optionally, the filtration combination can be preceded by a differentialcentrifugation, at low centrifugal force, to remove some portion of thebacterial cells and thereby enrich the supernatant for minicells.

Another purification method employs density gradient centrifugation in abiologically compatible medium. After centrifugation, a minicell band iscollected from the gradient, and, optionally, the minicells aresubjected to further rounds of density gradient centrifugation tomaximize purity. The method may further include a preliminary step ofperforming differential centrifugation on the minicell-containingsample. When performed at low centrifugal force, differentialcentrifugation will remove some portion of parent bacterial cells,thereby enriching the supernatant for minicells.

Particularly effective purification methods exploit bacterialfilamentation to increase minicell purity. Thus a minicell purificationmethod can include the steps of (a) subjecting a sample containingminicells to a condition that induces parent bacterial cells to adopt afilamentous form, followed by (b) filtering the sample to obtain apurified minicell preparation.

Known minicell purification methods also can be combined. One highlyeffective combination of methods is as follows:

Step A: Differential centrifugation of a minicell producing bacterialcell culture. This step, which may be performed at 2000 g for about 20minutes, removes most parent bacterial cells, while leaving minicells inthe supernatant.

Step B: Density gradient centrifugation using an isotonic and non-toxicdensity gradient medium. This step separates minicells from manycontaminants, including parent bacterial cells, with minimal loss ofminicells. Preferably, this step is repeated within a purificationmethod.

Step C: Cross-flow filtration through a 0.45 μm filter to further reduceparent bacterial cell contamination.

Step D: Stress-induced filamentation of residual parent bacterial cells.This may be accomplished by subjecting the minicell suspension to any ofseveral stress-inducing environmental conditions.

Step E: Antibiotic treatment to kill parent bacterial cells.

Step F: Cross-flow filtration to remove small contaminants, such asmembrane blebs, membrane fragments, bacterial debris, nucleic acids,media components and so forth, and to concentrate the minicells. A 0.2μm filter may be employed to separate minicells from small contaminants,and a 0.1 μm filter may be employed to concentrate minicells.

Step G: Dead-end filtration to eliminate filamentous dead bacterialcells. A 0.45 um filter may be employed for this step.

Step H: Removal of endotoxin from the minicell preparation. Anti-Lipid Acoated magnetic beads may be employed for this step.

In another aspect, the invention provides a targeted drug deliverymethod that comprises bringing bispecific ligands into contact with (i)bacterially derived minicells that contain a drug molecule and (ii)mammalian cells. The bispecific ligands, having specificity for bothminicell and mammalian cell components, cause the minicells to bind tothe mammalian cells, such that the minicells are engulfed by themammalian cells, and the drug is released into the cytoplasm of themammalian cells.

The inventors found that this approach is broadly applicable to a rangeof mammalian cells, including cells that normally are refractory tospecific adhesion and endocytosis of minicells. For example, bispecificantibody ligands with anti-O-polysaccharide specificity on one arm andanti-HER2 receptor, anti-EGF receptor or anti-androgen receptorspecificity on the other arm efficiently bind minicells to therespective receptors on a range of target non-phagocytic cells. Thesecells include lung, ovarian, brain, breast, prostate and skin cancercells. Moreover, the efficient binding precedes rapid endocytosis of theminicells by each of the non-phagocytic cells.

Target cells of the invention include any cell into which a drug is tobe introduced. “Introduced,” when used in reference to a drug, meansthat the drug carried within a minicell is delivered to the target cell,preferably intracellularly. Desirable target cells are characterized byexpression of a cell surface receptor that, upon binding of a ligand,facilitates endocytosis. Preferred target cells are non-phagocytic,meaning that the cells are not professional phagocytes, such asmacrophages, dendritic cells and Natural Killer (NK) cells. Preferredtarget cells also are mammalian.

Ligands useful in the targeted drug delivery methods of this inventioninclude any agent that binds to a surface component on a target cell andto a surface component on a minicell. Preferably, the surface componenton a target cell is a receptor, especially a receptor capable ofmediating endocytosis. The ligands may comprise a polypeptide and/orcarbohydrate component. Antibodies are preferred ligands. For example, abispecific antibody that carries dual specificities for a surfacecomponent on bacterially derived intact minicells and for a surfacecomponent on target mammalian cells, can be used efficiently to targetthe minicells to the target mammalian cells in vitro and in vivo. Usefulligands also include receptors, enzymes, binding peptides,fusion/chimeric proteins and small molecules.

The selection of a particular ligand is made on two primary criteria:(i) specific binding to one or more domains on the surface of intactminicells and (ii) specific binding to one or more domains on thesurface of the target cells. Thus, ligands preferably have a first armthat carries specificity for a bacterially derived intact minicellsurface structure and a second arm that carries specificity for amammalian cell surface structure. Each of the first and second arms maybe multivalent. Preferably, each arm is monospecific, even ifmultivalent.

For binding to bacterially derived minicells, it is desirable for onearm of the ligand to be specific for the O-polysaccharide component of alipopolysaccharide found on the parent bacterial cell. Other minicellsurface structures that can be exploited for ligand binding include cellsurface-exposed polypeptides and carbohydrates on outer membranes, suchas pilli, fimbrae and flagella cell surface exposed peptide segments.

For binding to target cells, one arm of the ligand is specific for asurface component of a mammalian cell. Such components include cellsurface proteins, peptides and carbohydrates, whether characterized oruncharacterized. Cell surface receptors, especially those capable ofactivating receptor-mediated endocytosis, are desirable cell surfacecomponents for targeting. Such receptors, if over-expressed on thetarget cell surface, confer additional selectivity for targeting thecells to be treated, thereby reducing the possibility for delivery tonon-target cells.

By way of example, one may target tumor cells, metastatic cells,vasculature cells, such as endothelial cells and smooth muscle cells,lung cells, kidney cells, blood cells, bone marrow cells, brain cells,liver cells, and so forth, or precursors of any selected cell byselecting a ligand that specifically binds a cell surface receptor motifon the desired cells. Examples of cell surface receptors includecarcinoembryonic antigen (CEA), which is overexpressed in most colon,rectum, breast, lung, pancreas and gastrointestinal tract carcinomas(Marshall, 2003); heregulin receptors (HER-2, neu or c-erbB-2), which isfrequently overexpressed in breast, ovarian, colon, lung, prostate andcervical cancers (Hung et al., 2000); epidermal growth factor receptor(EGFR), which is highly expressed in a range of solid tumors includingthose of the breast, head and neck, non-small cell lung and prostate(Salomon et al., 1995); asialoglycoprotein receptor (Stockert, 1995);transferrin receptor (Singh, 1999); serpin enzyme complex receptor,which is expressed on hepatocytes (Ziady et al., 1997); fibroblastgrowth factor receptor (FGFR), which is overexpressed on pancreaticductal adenocarcinoma cells (Kleeff et al., 2002); vascular endothelialgrowth factor receptor (VEGFR), for anti-angiogenesis gene therapy(Becker et al., 2002 and Hoshida et al., 2002); folate receptor, whichis selectively overexpressed in 90% of nonmucinous ovarian carcinomas(Gosselin and Lee, 2002); cell surface glycocalyx (Batra et al., 1994);carbohydrate receptors (Thurnher et al., 1994); and polymericimmunoglobulin receptor, which is useful for gene delivery torespiratory epithelial cells and attractive for treatment of lungdiseases such as Cystic Fibrosis (Kaetzel et al., 1997).

In a further example, anti-viral, anti-microbial and anti-parasiticdrugs can be incorporated into intact minicells and targeted delivery ofthe drugs can be achieved to specific infected cells, such asHIV-infected helper CD4+ T-lymphocytes.

Preferred ligands comprise antibodies and/or antibody derivatives. Asused herein, the term “antibody” encompasses an immunoglobulin moleculeobtained by in vitro or in vivo generation of an immunogenic response.The term “antibody” includes polyclonal, monospecific and monoclonalantibodies, as well as antibody derivatives, such as single-chainantibody fragments (scFv). Antibodies and antibody derivatives useful inthe present invention also may be obtained by recombinant DNAtechniques.

Wild type antibodies have four polypeptide chains, two identical heavychains and two identical light chains. Both types of polypeptide chainshave constant regions, which do not vary or vary minimally amongantibodies of the same class, and variable regions. Variable regions areunique to a particular antibody and comprise an antigen binding domainthat recognizes a specific epitope. The regions of the antigen bindingdomain that are most directly involved in antibody binding are“complementarity-determining regions” (CDRs).

The term “antibody” also encompasses derivatives of antibodies, such asantibody fragments that retain the ability to specifically bind toantigens. Such antibody fragments include Fab fragments (a fragment thatcontains the antigen-binding domain and comprises a light chain and partof a heavy chain bridged by a disulfide bond), Fab′ (an antibodyfragment containing a single antigen-binding domain comprising a Fab andan additional portion of the heavy chain through the hinge region,F(ab′)2 (two Fab′ molecules joined by interchain disulfide bonds in thehinge regions of the heavy chains), a bispecific Fab (a Fab moleculehaving two antigen binding domains, each of which may be directed to adifferent epitope), and an scFv (the variable, antigen-bindingdeterminative region of a single light and heavy chain of an antibodylinked together by a chain of amino acids.)

When antibodies, including antibody fragments, constitute part or all ofthe ligands, they preferably are of human origin or are modified to besuitable for use in humans. So-called “humanized antibodies” are wellknown in the art. See, e.g., Osbourn et al., 2003. They have beenmodified by genetic manipulation and/or in vitro treatment to reducetheir antigenicity in a human. Methods for humanizing antibodies aredescribed, e.g., in U.S. Pat. Nos. 6,639,055, 5,585,089, and 5,530,101.In the simplest case, humanized antibodies are formed by grafting theantigen-binding loops, known as complementarity-determining regions(CDRs), from a mouse mAb into a human IgG. See Jones et al., 1986;Riechmann et al., 1988; and Verhoeyen et al., 1988. The generation ofhigh-affinity humanized antibodies, however, generally requires thetransfer of one or more additional residues from the so-called frameworkregions (FRs) of the mouse parent mAb. Several variants of thehumanization technology also have been developed. See Vaughan et al.,1998.

Human antibodies, rather than “humanized antibodies,” also may beemployed in the invention. They have high affinity for their respectiveantigens and are routinely obtained from very large, single-chainvariable fragments (scFvs) or Fab phage display libraries. See Griffithset al., 1994; Vaughan et al., 1996; Sheets et al., 1998; de Haard etal., 1999; and Knappik et al., 2000.

Useful ligands also include bispecific single chain antibodies, whichtypically are recombinant polypeptides consisting of a variable lightchain portion covalently attached through a linker molecule to acorresponding variable heavy chain portion. See U.S. Pat. Nos.5,455,030; 5,260,203 and 4,496,778. Bispecific antibodies also can bemade by other methods. For example, chemical heteroconjugates can becreated by chemically linking intact antibodies or antibody fragments ofdifferent specificities. See Karpovsky et al., 1984. However, suchheteroconjugates are difficult to make in a reproducible manner and areat least twice as large as normal monoclonal antibodies. Bispecificantibodies also can be created by disulfide exchange, which involvesenzymatic cleavage and reassociation of the antibody fragments. SeeGlennie et al., 1987.

Because Fab and scFv fragments are monovalent they often have lowaffinity for target structures. Therefore, preferred ligands made fromthese components are engineered into dimeric, trimeric or tetramericconjugates to increase functional affinity. See Tomlinson and Holliger,2000; Carter, 2001; Hudson and Souriau, 2001; and Todorovska et al.,2001. Such conjugate structures may be created by chemical and/orgenetic cross-links.

Bispecific ligands of the invention preferably are monospecific at eachend, i.e., specific for a single component on minicells at one end andspecific for a single component on target cells at the other end. Theligands may be multivalent at one or both ends, for example, in the formof so-called diabodies, triabodies and tetrabodies. See Hudson andSouriau, 2003. A diabody is a bivalent dimer formed by a non-covalentassociation of two scFvs, which yields two Fv binding sites. Likewise, atriabody results from the formation of a trivalent trimer of threescFvs, yielding three binding sites, and a tetrabody results from theformation of a tetravalent tetramer of four scFvs, yielding four bindingsites.

Several humanized, human, and mouse monoclonal antibodies and fragmentsthereof that have specificity for receptors on mammalian cells have beenapproved for human therapeutic use, and the list is growing rapidly. SeeHudson and Souriau, 2003. An example of such an antibody that can beused to form one arm of a bispecific ligand has specificity for HER2:Herceptin™; Trastuzumab.

Antibody variable regions also can be fused to a broad range of proteindomains. Fusion to human immunoglobulin domains such as IgG1 CH3 bothadds mass and promotes dimerization. See Hu et al., 1996. Fusion tohuman Ig hinge-Fc regions can add effector functions. Also, fusion toheterologous protein domains from multimeric proteins promotesmultimerization. For example, fusion of a short scFv to shortamphipathic helices has been used to produce miniantibodies. See Packand Pluckthun, 1992. Domains from proteins that form heterodimers, suchas fos/jun, can be used to produce bispecific molecules (Kostelny etal., 1992) and, alternately, homodimerization domains can be engineeredto form heterodimers by engineering strategies such as “knobs intoholes” (Ridgway et al., 1996). Finally, fusion protein partners can beselected that provide both multimerization as well as an additionalfunction, e.g. streptavidin. See Dubel et al., 1995.

In another aspect, the invention provides a composition of matter usefulfor introducing drug molecules into target mammalian cells with highefficiency. The composition comprises (i) a bacterially derived minicelland (ii) a bispecific ligand. The minicell and ligand may be any ofthose described herein. Thus, the minicell contains a drug and thebispecific ligand preferably is capable of binding to a surfacecomponent of the minicell and to a surface component of a targetmammalian cell.

A composition consisting essentially of minicells and bispecific ligandsof the present invention (that is, a composition that includes suchminicells and ligands with other constituents that do not interfereunduly with the drug-delivering quality of the composition) can beformulated in conventional manner, using one or more pharmaceuticallyacceptable carriers or excipients.

The term “pharmaceutically acceptable” means that a carrier or excipientdoes not abrogate biological activity of the composition beingadministered, is chemically inert and is not toxic to the organism inwhich it is administered. Formulations may be presented in unit dosageform, e.g., in ampules or vials, or in multi-dose containers, with orwithout an added preservative. The formulation can be a solution, asuspension, or an emulsion in oily or aqueous vehicles, and may containformulatory agents, such as suspending, stabilizing and/or dispersingagents. A suitable solution is isotonic with the blood of the recipientand is illustrated by saline, Ringer's solution, and dextrose solution.Alternatively, compositions may be in lyophilized powder form, forreconstitution with a suitable vehicle, e.g., sterile, pyrogen-freewater or physiological saline. The compositions also may be formulatedas a depot preparation. Such long-acting formulations may beadministered by implantation (for example, subcutaneously orintramuscularly) or by intramuscular injection.

A composition of the present invention can be administered via variousroutes and to various sites in a mammalian body, to achieve thetherapeutic effect(s) desired, either locally or systemically. Deliverymay be accomplished, for example, by oral administration, by applicationof the formulation to a body cavity, by inhalation or insufflation, orby parenteral, intramuscular, intravenous, intraportal, intrahepatic,peritoneal, subcutaneous, intratumoral, or intradermal administration.The mode and site of administration is dependent on the location of thetarget cells. For example, cystic-fibrotic cells may be efficientlytargeted by inhaled delivery of the targeted recombinant minicells.Similarly, tumor metastasis may be more efficiently treated viaintravenous delivery of targeted recombinant minicells. Primary ovariancancer may be treated via intraperitoneal delivery of targetedrecombinant minicells.

The present invention further provides for drug delivery by means ofbringing bacterially derived minicells, which contain a drug, intocontact with mammalian cells that are phagocytosis- orendocytosis-competent. Such mammalian cells, which are capable ofengulfing parent bacterial cells in the manner of intracellularbacterial pathogens, likewise engulf the minicells, which release theirdrug payload into the cytoplasm of the mammalian cells. Thisdrug-delivery approach can be effected without the use a targetingligands.

A variety of mechanisms may be involved in the engulfing of minicells bya given type of cell, and the present invention is not dependent on anyparticular mechanism in this regard. For example, phagocytosis is awell-documented process in which macrophages and other phagocyte cells,such as neutrophils, ingest particles by extending pseudopodia over theparticle surface until the particle is totally enveloped. Althoughdescribed as “non-specific” phagocytosis, the involvement of specificreceptors in the process has been demonstrated. See Wright & Jong(1986); Speert et al. (1988).

Thus, one form of phagocytosis involves interaction between surfaceligands and ligand-receptors located at the membranes of the pseudopodia(Shaw and Griffin, 1981). This attachment step, mediated by the specificreceptors, is thought to be dependent on bacterial surface adhesins.With respect to less virulent bacteria, such as non-enterotoxigenic E.coli, phagocytosis also may occur in the absence of surface ligands forphagocyte receptors. See Pikaar et al. (1995), for instance. Thus, thepresent invention encompasses but is not limited to the use of minicellsthat either possess or lack surface adhesins, in keeping with the natureof their parent bacterial cells, and are engulfed by phagocytes (i.e.,“phagocytosis-competent” host cells), of which neutrophils andmacrophages are the primary types in mammals.

Another engulfing process is endocytosis, by which intracellularpathogens exemplified by species of Salmonella, Escherichia, Shigella,Helicobacter, Pseudomonas and Lactobacilli gain entry to mammalianepithelial cells and replicate there. Two basic mechanisms in thisregard are Clathrin-dependent receptor-mediated endocytosis, also knownas “coated pit endocytosis” (Riezman, 1993), and Clathrin-independentendocytosis (Sandvig & Deurs, 1994). Either or both may be involved whenan engulfing-competent cell that acts by endocytosis (i.e., an“endocytosis-competent” host cell) engulfs minicells in accordance withthe invention. Representative endocytosis-competent cells are breastepithelial cells, enterocytes in the gastrointestinal tract, stomachepithelial cells, lung epithelial cells, and urinary tract and bladderepithelial cells.

When delivering a drug to an engulfing-competent mammalian cell withoutthe use of a targeting ligand, the nature of the applicationcontemplated will influence the choice of bacterial source for theminicells employed. For example, Salmonella, Escherichia and Shigellaspecies carry adhesins that are recognized by endocytosis-mediatingreceptors on enterocytes in the gastrointestinal tract, and may besuitable to deliver a drug that is effective for colon cancer cells.Similarly, minicells derived from Helicobacter pylori, carrying adhesinsspecific for stomach epithelial cells, could be suited for deliveryaimed at stomach cancer cells. Inhalation or insufflation may be idealfor administering intact minicells derived from a Pseudomonas speciesthat carry adhesins recognized by receptors on lung epithelial cells.Minicells derived from Lactobacilli bacteria, which carry adhesinsspecific for urinary tract and bladder epithelial cells, could bewell-suited for intraurethral delivery of a drug to a urinary tract or abladder cancer. The invention also provides for the use of bacteriallyderived intact minicells and bispecific ligands in preparing medicamentfor use in a method of treating disease or modifying a trait byadministration of the medicament to a cell, tissue or organ. In themedicament, minicells contain a drug molecule and bispecific ligands arecapable of binding to the minicells and to target mammalian cells. Suchmedicaments are useful to treat various conditions and diseases,including acquired diseases such as AIDS, pneumonia and tuberculosis,but are particularly useful in the context of cancer chemotherapy.

The invention further provides methods of loading minicells with a drug.Using these methods, drug packaging can be accomplished for bothhydrophilic and hydrophobic drugs. One method of loading minicells witha drug involves creating a concentration gradient of the drug between anextracellular medium containing the minicells and the minicellcytoplasm. When the extracellular medium contains a higher drugconcentration than the minicell cytoplasm, the drug naturally moves downthis concentration gradient, into the minicell cytoplasm. When theconcentration gradient is reversed, however, the drug does not move outof the minicells.

That therapeutically significant amounts of drugs can be packaged thuslyin non-living minicells without leakage is surprising for severalreasons. It is known that the outer envelope of live bacteria, bothGram-negative and Gram-positive, forms an effective barrier to solutesin the surrounding medium, while being permeable to water. This protectsthe bacteria from deleterious effects of toxic molecules, such asbiocides and antibiotics. It is also known that the bacterial envelopeconfers intrinsic resistance to the passive diffusion and intracellularentry of hydrophobic chemicals that cannot enter through water filledhydrophilic channels, formed by membrane-associated proteins calledporins.

Minicells contain the same outer envelope as their parent bacterialcells. Thus, it is surprising that both hydrophilic drugs, exemplifiedby Doxorubicin and Vinblastine, and hydrophobic drugs, exemplified byPaclitaxel, can be readily transferred into the minicell cytoplasm bycreating a simple concentration gradient of the drug between theextra-minicell and intra-minicell environments. This suggests that theenvelope permeability of non-living bacteria and their derivatives isquite different from the envelope permeability of living bacteria.

The discovery that drug movement occurs only in one direction inminicells was a greater surprise. It is well established that livebacteria have active efflux processes to remove toxic chemical entitiesthat happen to enter their cytoplasm (reviewed by Borges-Walmsley andWalmsley, 2001). These processes are mediated by multidrug transporters,a large and diverse group of proteins capable of protecting cellsagainst a wide variety of environmental toxins by active extrusion ofnoxious compounds. There are at least five known families, based onsequence similarity, of multidrug transporters. They include the (i)major facilitator (MFS), (ii) resistance-nodulation-cell division (RND),(iii) small multidrug resistance, (iv) multidrug and toxic compoundextrusion, and (v) ATP-binding cassette families. These multidrugtransporters are bacterial membrane bound proteins and are widelydistributed in bacterial species.

Multidrug transporters should be conserved in minicell membranes, yetthey surprisingly appear to be non-functional, possibly becauseminicells are non-living and lack the ATP necessary to drive multidrugtransporters.

To load minicells with drugs that normally are not water soluble, thedrugs initially can be dissolved in an appropriate solvent. For example,Paclitaxel can be dissolved in a 1:1 blend of ethanol and cremophore EL(polyethoxylated castor oil), followed by a dilution in PBS to achieve asolution of Paclitaxel that is partly diluted in aqueous media andcarries minimal amounts of the organic solvent to ensure that the drugremains in solution. Minicells can be incubated in this final medium fordrug loading. Thus, the inventors discovered that even hydrophobic drugscan diffuse into the cytoplasm of minicells to achieve a high andtherapeutically significant cytoplasmic drug load. This is unexpectedbecause the minicell membrane is composed of a hydrophobic phospholipidbilayer, which would be expected to prevent diffusion of hydrophobicmolecules into the cytoplasm.

Another method of loading minicells with a drug involves culturing arecombinant parent bacterial cell under conditions wherein the parentbacterial cell transcribes and translates a therapeutic nucleic acidencoding the drug, such that the drug is released into the cytoplasm ofthe parent bacterial cell. For example, a gene cluster encoding thecellular biosynthetic pathway for a desired drug can be cloned andtransferred into a parent bacterial strain that is capable of producingminicells. Genetic transcription and translation of the gene clusterresults in biosynthesis of the drug within the cytoplasm of the parentbacterial cells, filling the bacterial cytoplasm with the drug. When theparent bacterial cell divides and forms progeny minicells, the minicellsalso contain the drug in their cytoplasm. The pre-packaged minicells canbe purified by any of the minicell purification processes known in theart and described above.

Similarly, another method of loading minicells with a drug involvesculturing a recombinant minicell that contains an expression plasmidencoding the drug under conditions such that the gene encoding the drugis transcribed and translated within the minicell.

For producing drugs directly within parent bacterial cells or minicells,the parent bacterial cells or minicells contain a nucleic acid moleculethat, upon transcription and/or translation, function to ameliorate orotherwise treat a disease or modify a trait in a cell, tissue or organ.For purposes of the present description, such nucleic acid molecules arecategorized as “therapeutic nucleic acid molecules.” Ordinarily, thetherapeutic nucleic acid is found on a plasmid within the parentbacteria or minicells.

The therapeutic nucleic acid molecule encodes a drug product, such asfunctional RNA (e.g., antisense or siRNA) or a peptide, polypeptide orprotein, the production of which is desired. For example, the geneticmaterial of interest can encode a hormone, receptor, enzyme, or (poly)peptide of therapeutic value. A therapeutic nucleic acid molecule may bethe normal counterpart of a gene that expresses a protein that functionsabnormally or that is present in abnormal levels in a disease state, asis the case, for example, with the cystic fibrosis transmembraneconductance regulator in cystic fibrosis (Kerem et al., 1989; Riordan etal., 1989; Rommens et al., 1989), with β-globin in sickle-cell anemia,and with any of α-globin, β-globin and γ-globin in thalassemia. Thetherapeutic nucleic acid molecule can have an antisense RNA transcriptor small interfering RNA, as mentioned above.

In the treatment of cancer, a therapeutic nucleic acid molecule suitablefor use according to the present invention could have a sequence thatcorresponds to or is derived from a gene that is associated with tumorsuppression, such as the p53 gene, the retinoblastoma gene, and the geneencoding tumor necrosis factor. A wide variety of solid tumors—cancer,papillomas, and warts—should be treatable by this approach, pursuant tothe invention. Representative cancers in this regard include coloncarcinoma, prostate cancer, breast cancer, lung cancer, skin cancer,liver cancer, bone cancer, ovary cancer, pancreas cancer, brain cancer,head and neck cancer, and lymphoma. Illustrative papillomas are squamouscell papilloma, choroid plexus papilloma and laryngeal papilloma.Examples of wart conditions are genital warts, plantar warts,epidermodysplasia verruciformis, and malignant warts.

A therapeutic nucleic acid molecule for the present invention also cancomprise a DNA segment coding for an enzyme that converts an inactiveprodrug into one or more cytotoxic metabolites so that, upon in vivointroduction of the prodrug, the target cell in effect is compelled,perhaps with neighboring cells as well, to commit suicide. Preclinicaland clinical applications of such a “suicide gene,” which can be ofnon-human origin or human origin, are reviewed by Spencer (2000),Shangara et al. (2000) and Yazawa et al. (2002). Illustrative of suicidegenes of non-human origin are those that code for HSV-thymidine kinase(tk), cytosine deaminase (CDA)+uracil phosphoribosytransferase,xanthine-guanine phosphoribosyl-transferase (GPT), nitroreductase (NTR),purine nucleoside phophrylase (PNP, DeoD), cytochrome P450 (CYP4B1),carboxypeptidase G2 (CPG2), and D-amino acid oxidase (DAAO),respectively. Human-origin suicide genes are exemplified by genes thatencode carboxypeptidase A1 (CPA), deoxycytidine kinase (dCK), cytochromeP450 (CYP2B1,6), LNGFR/FKBP/Fas, FKBP/Caspases, and ER/p53,respectively.

According to the invention, the therapeutic nucleic acid typically iscontained on a plasmid within the parent bacterial cell or minicell. Theplasmid also may contain an additional nucleic acid segment thatfunctions as a regulatory element, such as a promoter, a terminator, anenhancer or a signal sequence, and that is operably linked to thetherapeutic nucleic acid segment.

A plasmid within a parent bacterial cell or minicell of the inventionalso may contain a reporter element. A reporter element confers on itsrecombinant host a readily detectable phenotype or characteristic,typically by encoding a polypeptide, not otherwise produced by the host,that can be detected, upon expression, by histological or in situanalysis, such as by in vivo imaging techniques. For example, a reporterelement delivered by an intact minicell, according to the presentinvention, could code for a protein that produces, in the engulfing hostcell, a colorimetric or fluorometric change that is detectable by insitu analysis and that is a quantitative or semi-quantitative functionof transcriptional activation. Illustrative of these proteins areesterases, phosphatases, proteases and other enzymes, the activity ofwhich generates a detectable chromophore or fluorophore.

Preferred examples are E. coli β-galactosidase, which effects a colorchange via cleavage of an indigogenic substrate,indolyl-β-D-galactoside, and a luciferase, which oxidizes a long-chainaldehyde (bacterial luciferase) or a heterocyclic carboxylic acid(luciferin), with the concomitant release of light. Also useful in thiscontext is a reporter element that encodes the green fluorescent protein(GFP) of the jellyfish, Aequorea victoria, as described by Prasher etal. (1995). The field of GFP-related technology is illustrated by twopublished PCT applications, WO 095/21191 (discloses a polynucleotidesequence encoding a 238 amino-acid GFP apoprotein, containing achromophore formed from amino acids 65 through 67) and WO 095/21191(discloses a modification of the cDNA for the apopeptide of A. victoriaGFP, providing a peptide having altered fluorescent properties), and bya report of Heim et al. (1994) of a mutant GFP, characterized by a4-to-6-fold improvement in excitation amplitude.

The following examples illustrate provide a more complete understandingof the invention and are illustrative only.

EXAMPLE 1 Efficient Packaging of the Hydrophilic Cancer ChemotherapeuticDrugs Doxorubicin and Vinblastine in Bacterially Derived IntactMinicells

This example demonstrates that hydrophilic drugs can be packaged intothe cytoplasm of bacterially derived intact minicells.

Doxorubicin is a strong antimitogenic anthracycline antibiotic isolatedfrom Streptomyces peucetius, and is commonly employed for treatingbreast carcinoma (Henderson et al., 1989; Cowan et al., 1991; Chan etal., 1999; Paridaens et al., 2000; Norris et al., 2000). Even with theavailability of taxanes and other new agents, Doxorubicin remains amainstay of treatment for patients with metastatic disease.

Vinca alkaloids constitute a chemical class of major interest in cancerchemotherapy. The lead compounds, Vinblastine and Vincristine, have beenemployed in clinical practice for more than thirty years and remainwidely used to this day. Vinblastine inhibits cell proliferation bycapping microtubule ends, thereby suppressing mitotic spindlemicrotubule dynamics.

Minicells were obtained from an S. typhimurium minCDE-mutant straingenerated previously, as described in international application No.PCT/IB02/04632, and were purified via a gradientcentrifugation/filamentation/filtration/endotoxin removal proceduredescribed above.

Drug was packaged into the minicells by creating a concentrationgradient of the drug between the extracellular and intracellularcompartments. Drug moved down this gradient and into the minicellcytoplasm, through the intact minicell membrane.

The purified minicells were packaged with chemotherapeutic drugDoxorubicin (Sigma Chemical Company, St. Louis, Mo., USA) as follows.7×10⁹ minicells in BSG solution were centrifuged, the supernatant wasdiscarded and the minicells were resuspended in 940 ul BSG and 60 ul ofDoxorubicin solution (1 mg/ml; dissolved in sterile distilled water).The suspension was incubated overnight at 37° C. with rotation to allowthe Doxorubicin to diffuse into the minicell cytoplasm. ExcessDoxorubicin non-specifically attached to the outer surface of theminicells was then washed away by stirred cell ultrafiltration asfollows. Amicon stirred ultrafiltration cell Model 8010 (Millipore,Billerica, Mass., USA) was assembled according to the manufacturer'sinstructions with an ultrafiltration membrane disc (polyethersulfone;molecular weight cut-off of 300 kDa; Millipore). The cell was washedthree times with sterile distilled water followed by a further threewashes with BSG. The cell was then filled with 9 ml of fresh BSG and the1 ml solution of Doxorubicin-packaged minicells was added. The cell waskept under a pressure of 10 psi, stirred until the volume was reduced to5 ml and topped-off with 5 ml BSG. Ultrafiltration was continued untilthe volume again dropped to 5 ml. This topping-off/ultrafiltrationprocedure was performed 6 times to enable a thorough washing of theexterior surfaces of the Doxorubicin-packaged minicells. During the lastultrafiltration, the volume was reduced to 1 ml and the sample wastransferred to a sterile Eppendorf centrifuge tube, followed bycentrifugation at 13,200 rpm for 10 minutes to pellet theDoxorubicin-packaged minicells.

Doxorubicin-packaged minicells were mounted on glass slides and werevisualized using a fluorescence microscope (Leica model DM LB lightmicroscope, 100× magnification; Leica Microsystems, Germany) becauseDoxorubicin is intrinsically fluorescent. The results were capturedusing the Leica DC camera and Leica IM image management software. Theappropriate filter was used to permit visualization of Doxorubicin'sautofluorescence (excitation 488 nm, emission 550 nm; red fluorescence).

The results revealed that all the minicells fluoresced bright redsuggesting that the Doxorubicin had been transferred into the minicellcytoplasm and, despite the extensive washing steps using the stirredcell ultrafiltration system, the Doxorubicin was unable to diffuse outof the minicell cytoplasm. This was surprising because, during thewashing steps, the concentration gradient of Doxorubicin had beenreversed, i.e., the Doxorubicin concentration in the minicell cytoplasmwas higher than that of extracellular environment (BSG solution).Control minicells that were not incubated with the drug did not show anybackground autofluorescence.

To demonstrate that drug-packaging in minicells is not limited todoxorubicin, similar experiments were performed with another cancerchemotherapeutic drug, Vinblastine, that has low solubility in water.This drug does not autofluoresce; hence BODIPY-FL-conjugated Vinblastine(Molecular Probes, Eugene, Oreg., USA), a fluorescent analog, was used(excitation 505 nm, emission 513 nm; red fluorescence). The purifiedminicells were packaged with BODIPY-FL-conjugated Vinblastine asfollows: the drug was initially dissolved in methanol (stock solution of10 mg/ml) and diluted 1:10 in sterile PBS to give a stock solution of 1mg/ml. 7×10⁹ minicells in BSG solution were centrifuged, supernatant wasdiscarded and the minicells were resuspended in 940 ul BSG and 60 ul ofBODIPY-FL-conjugated Vinblastine solution (1 mg/ml stock solution). Thisgave a final concentration of 60 ug of drug in 1 ml of minicellsuspension. The suspension was incubated overnight at 37° C. withrotation to allow the drug to diffuse into the minicell cytoplasm. Thesubsequent procedures of washing the excess drug by ultrafiltration upto the stage of final resuspension of drug-packaged minicells in BSGprior to visualization by fluorescence microscopy were the same asdescribed above for Doxorubicin.

The drug-packaged minicells were mounted on glass slides and werevisualized using a fluorescence microscope as above and the results werecaptured using the Leica DC camera and Leica IM image managementsoftware. The appropriate filter was used to permit visualization of redfluorescence of BODIPY-FL-conjugated Vinblastine.

The results revealed that all the minicells fluoresced bright red,indicating that the drug had been transferred into the minicellcytoplasm and, similarly to the observations for Doxorubicin, that theextensive washing steps, using the stirred cell ultrafiltration system,did not result in an efflux of the drug from the minicells into theextracellular fluid. This was surprising, too, because it isconventional wisdom thought that only highly hydrophilic solutes canenter into a bacterial cell via diffusion, possibly through porinchannels found in bacterial membranes. The present results show,however, that even drugs that are not highly hydrophilic can diffusethrough the membrane of a non-living bacterial cell derivative, such asa minicell. Control minicells that were not incubated with the drug didnot show any background autofluorescence.

EXAMPLE 2 Efficient Packaging of the Hydrophobic Cancer ChemotherapeuticDrug Paclitaxel in Bacterially Derived Intact Minicells

This example shows that hydrophobic drugs can be packaged into thecytoplasm of bacterially derived intact minicells. Because the minicellsurface membrane is composed of a phospholipid bilayer, diffusion ofhighly hydrophobic drugs across this barrier would not be expected.

Taxol (Paclitaxel; registered trademark of Bristol-Myers Squibb Company)is a tricyclic diterpene originally isolated from the bark of a Pacificyew tree, and more recently from the needles of the western yew treeTaxus brevifolia. Paclitaxel is one of the most importantchemotherapeutic agents, having promising antitumor activity, especiallyagainst ovarian, breast, and lung cancers (Mekhail and Markman, 2002).Paclitaxel is an antimitotic agent that binds to tubulin in a 1:1stoichiometry with tubulin heterodimers stabilizing microtubules anddriving a high percentage of cells to arrest in the G₂/M phase, progressslowly in the cell cycle without cytokinesis, form multinucleatedpolyploid cells, and undergo apoptosis. Paclitaxel has an extremely lowaqueous solubility of 0.00025 mg/ml and has to be solubilized in certaincosolvents such as 50% Cremophore EL and 50% Ethanol.

To demonstrate that a hydrophobic drug like Paclitaxel could betransported into the minicell cytoplasm, a fluorescent derivative ofPaclitaxel, Oregon Green® 488 conjugated Paclitaxel (Molecular Probes,Eugene, Oreg., USA; absorbance 496 nm, emission 524 nm) was used. Twodifferent methods were adopted to solubilize the drug: (i) in ethanol(to give a 7.58 mM stock solution), and (ii) in ethanol:cremophore EL(1:1 vol/vol; 3.79 mM stock solution). Each stock solution was diluted1:10 (vol/vol) in PBS to give 758 uM and 379 uM stock solutions,respectively. The latter stock solutions were added to the minicellsuspension (10⁹ minicells) at a 1:20 dilution to give a finalconcentration of Oregon Green® 488 conjugated Paclitaxel concentrationin the minicell extracellular environment of 40 uM and 20 uM,respectively. The minicells were incubated with the drug at 37° C.overnight with rotation and subsequently washed with ultrafiltration asdescribed in Example 1 for Doxorubicin and Vinblastine. The minicellswere resuspended and visualised by fluorescence microscopy, also asdescribed in Example 1.

The results revealed that all minicells fluoresced bright green,suggesting that both methods enabled the transfer of Paclitaxel from theextracellular milieu via the minicell membrane and into the cytoplasm ofthe minicell. This was surprising because it was not expected that thehighly hydrophobic drug would diffuse into the minicell cytosol via thephospholipid bilayer (hydrophobic) membrane of the minicell.Additionally, similar to the observations in the experiments in Example1, the reversal of the osmotic gradient during the extensive washingsteps did not cause efflux of the drug out of the minicell cytoplasm.

The results in Examples 1 and 2 demonstrate that the simple techniquesdescribed above can be used to readily package both hydrophilic andhydrophobic drugs into minicell drug delivery vehicles.

EXAMPLE 3 Methods for Determining the Drug Concentration in BacteriallyDerived Intact Minicells

This example demonstrates a method for determining the concentration ofa drug in bacterially derived intact minicells. More particularly, theexample describes a method for determining the concentration ofDoxorubicin present in minicells_(DOX), and demonstrates the effect ofDoxorubicin concentration in a loading solution. The application ofdrug-packaged minicells for therapeutic purposes requires the ability tocharacterize a packaged drug entity, including determining the quantityof packaged drug. Previously, however, there were no methods foreffectively disrupting bacterially derived intact minicells or bacterialcells and extracting packaged drug molecules.

Abbreviations used below include (i) HCl; Hydrochloric acid (BDH ARMERCK, Australia), (ii) MeCN; Acetonitrile, Pesticide Residue grade(Burdick & Jackson, Mich., USA), (iii) IPA; Isopropyl alcohol or2-propanol, Pesticide Residue grade (Burdick & Jackson), MQ; MilliQpolished RO water (R≧10¹⁸Ω), C18 & RP18; refer to the stationary phasepacking chemistry present in the chromatography column (in this case itis an 18 carbon long hydrocarbon chain bonded to the silanol end groupof the 5 micron (μm) diameter silica particles), (iv) HPLC & LC; Highperformance liquid chromatography, (v) MS; Mass spectrometry, (vi)MS/MS; Collision induced fragmentation of a selected parent ion toproduce a defined daughter ion (useful in removing matrix effects andincreasing signal/noise), (vii) ESI; Electrospray source ionisation (theion current is generated in thermo-pneumatic spray at the head of the MSinlet).

10⁹ intact minicells were separately incubated in a solution ofDoxorubicin at final concentrations of 5, 10, 20, 30, 40, 50, 60, 80,100, 120, 140, 160, 180, 200 and 250 μg/mL. The mixtures were incubatedat 37° C. overnight with rotation. The minicells were harvested bycentrifugation at 13,200 rpm/5 min and resuspended in sterile BSG. Theminicell suspension was placed in an Amicon filtration chamber (0.2 μmpore size) and washed 10 times with 10 ml of BSG per wash. The minicellswere collected and divided into duplicates of 5×10⁸ minicells forDoxorubicin extraction.

The minicells were centrifuged at 13,200 rpm, and supernatant wasdiscarded. To each pellet, 500 μL of 97 mM HCl-IPA was added, followedby 5 cycles of 1 minute vortexing and 1 minute sonication. MQ (500 μL)was added and the 5 cycles of 1 minute vortexing and 1 minute sonicationwere repeated. The extract was centrifuged for 5 mins at 13,200 rpm topellet debris, and the supernatant was transferred to a HPLC 150 μLglass insert and vial. Because Doxorubicin autofluoresces, an HPLCfluorescence-based analysis of the extracted drug was developed andperformed as follows. The HPLC method characteristics included (i)Mobile Phase: 100 mM ammonium formate+0.05% triethylamine (pH=3.5): MQ:MeCN was 28:42:30 @ 1 mL/min, (ii) Stationary Phase: Merck LichrosphereRP18, 5 μm, 4.0 mm×250 mm, (iii) Column Temperature: 40° C., (iv)Injection volume: 15 μL, (iv) Detection: Fluorescence—Excite 480 nm,Emission 550 nm, (v) HPLC system: A Shimadzu 10AVP system was used,comprising an autosampler, solvent degasser, quaternary pump, columnheater (40° C.) and fluorescence detector, running version 7.2 SPI rev Bsoftware. Shimadzu Corporation (Kyoto Japan).

Doxorubicin measurements were done using both HPLC and LC-MS to confirmthat the data were reliable. The LC-MS procedure and key characteristicsincluded (i) Mobile Phase: 5 mM ammonium formate (pH=3.5): MeCN=76:24 @0.2 mL/min, (ii) Stationary Phase: Phenomenex Luna C18 (2), 5 μm, 2.0mm×150 mm, (iii) Column Temperature: 30° C., (iv) Injection volume: 2μL, (v) LC and MS system: Both the LC and MS systems were fromThermo-Finnigan (Boston, Mass., USA). The LC system comprised anautosampler with integrated column heater and pump. The column eluentwas directly transferred to the electrospray ionization source of theThermo-Finnigan LCQ-Deca ion trap mass spectrometer, (vi) Detection: TheMS detector was operated in positive ion mode and MS/MS scan mode. Theparent ion was set at m/z=543.9, yielding a daughter ion at m/z=396.8.The daughter ion was tracked for quantitation purposes.

The three fluorescent determinations and the MS results were plottedtogether (FIG. 1) to indicate their equivalent [DOX] determinations(within the error bars of the measurements). The results showed a clearcorrelation between the Doxorubicin concentration extracted fromminicells_(DOX) and the external loading concentration of Doxorubicin.These experiments were repeated 3 times with similar results.Additionally, the techniques were adapted to determine the concentrationof other chemotherapeutic drugs like paclitaxel, Irinotecan,5-Fluorouracil and Cisplatin packaged in intact minicells.

EXAMPLE 4 Drugs and the Attachment of Surface Ligands do not CauseMinicell Instability or Loss of Membrane-Embedded Structures

This example demonstrates that the packaging of drugs in minicells andattachment of ligands to the surface of drug-packaged minicells does notcause minicell instability, drug leakage or a loss of minicellmembrane-embedded structures. The result is surprising because one wouldexpect that drugs, particularly highly noxious chemotherapeutic drugs,in the cytoplasm would destabilize the minicell bilayer membrane.

A study was designed to determine if the packaging of drugs in minicellsand/or the attachment of bispecific ligands to surface structures (e.g.O-antigen component of LPS) of minicells would cause drug leakage and/orloss of minicell bilayer-embedded structures with the bispecific ligand(e.g., LPS shedding). Minicells (5×10⁸) were packaged with eitherDoxorubicin or Oregon Green® 488-conjugated Paclitaxel (MolecularProbes, Eugene, Oreg., USA) as described above. The drug concentrationin the Minicells_(DOX) and minicells_(Pac) was determined as describedin Example 3, and the results showed 425 ng DOX and 245 ng Paclitaxel,respectively.

A BsAb with anti-S. Typhimurium O-antigen and anti-EGFR specificitieswas constructed as described in PCT/US2004/041010. Briefly, bispecificantibody (BsAb) was constructed by linking an anti-S. TyphimuriumO-antigen monoclonal antibody (MAb) (IgG1; Biodesign) and a MAb directedagainst a target cell-surface receptor that is mouse anti-human EGFR(IgG2a; Oncogene) or mouse anti-human HER2/neu receptor (IgG1; Serotec).The two antibodies were cross-linked via their Fc regions using purifiedrecombinant protein A/G (Pierce Biotechnology). Briefly, protein A/G(100 μg/ml final concentration) was added to 0.5 ml of a premixedsolution containing 20 μg/ml each of anti-S. Typhimurium O-antigen andanti-human EGFR MAbs, and incubated overnight at 4° C. Excess antibodieswere removed by incubation with protein G-conjugated magnetic beads andgentle mixing at room temperature for 40 min. After magnetic separationof the beads, the protein A/G-BsAb complex was incubated with 5×10⁸drug-packaged minicells for 1 hr at room temperature to coat them withantibody via binding of the O-antigen specific Fab arm to surface LPS.Alexa-Flour 488® (Molecular Probes; green fluorescence) or Alexa Fluor®594 (Molecular Probes; red fluorescence) was used to conjugate to theBsAb. The minicells_(DOX) were mixed with Alexa-Flour 488®-conjugatedBsAb and minicells_(Pac) were mixed with Alexa Fluor® 594-conjugatedBsAb. The various minicell preparations were visualized using a LeicaFluorescence microscope using 100× objective and the appropriate filtersfor red and green fluorescence.

The results showed that BsAb attachment to the minicell_(DOX) andminicell_(Pac) surface was intense, appearing as a complete ring aroundthe minicell cytoplasm. The individual drugs Doxorubicin and Paclitaxelalso were visualized within the minicell cytoplasm. The drugs wereextracted from the minicells as described above and the drugconcentrations were determined. The drug concentrations were the same inminicell_(DOX) and minicell_(Pac), compared with ^(EGFR)minicell_(DOX)and ^(EGFR)minicell_(Pac) (i.e., 425 ng Doxorubicin and 245 ngPaclitaxel, respectively).

Similar results were obtained using other BsAbs, such aanti-Oantigen/anti-HER2/neu. This suggested that the methods arecompatible with the development of a safe drug delivery vector, becausethe drug packaging and BsAb attachment did not result in instability ofthe vector or drug leakage from the intact minicell.

EXAMPLE 5 Targeted Delivery In-Vitro of Doxorubicin to Non-PhagocyticHuman Brain Cancer Cells Via Ligand-Targeted and Doxorubicin-PackagedMinicells

This example demonstrates that a chemotherapeutic drug, Doxorubicin,packaged in intact minicells carrying a cell surface-bound bispecificligand, can (a) specifically bind to a target non-phagocytic mammaliancell surface, the EGF receptor on human brain cancer cells, and (b)deliver the drug intracellularly within the mammalian cell followingendocytosis and breakdown of Doxorubicin-packaged minicells.

S. typhimurium minCDE-derived minicells were purified and packaged withDoxorubicin, as described in Example 1.

A bispecific antibody was constructed as described above and in U.S.patent application Ser. No. 10/602,021 and briefly described in example4.

The anti-EGFR monoclonal antibody was selected because the target cellsto be tested were human brain cancer cells U87-MG (ATCC, Rockville, Md.,USA; human malignant astrocytoma epithelial cell line) that are known tooverexpress the EGF receptor on the cell surface.

The bispecific antibody was tagged with a fluorescent dye to enablevisualization and tracking, by fluorescence confocal microscopy, of thetargeted minicells. The procedure was as follows. Alexa Fluor 488protein labeling kit (Molecular Probes, Eugene, Oreg., USA) was used tolabel the bispecific antibody. Alexa Fluor 488 dye (absorbance 494 nm,emission 519 nm; green fluorescence) was conjugated via the free aminegroups of the bispecific antibody according to the manufacturer'sinstructions.

U87-MG astrocytoma cells were grown on 15 mm coverslips in 12-welltissue culture plates (Genstar; Greiner Bio-One GmbH, Frickenhausen,Germany). Cells were grown in RPMI 1640 medium with 5% cosmic calf serum(Hyclone, Logan, Utah, USA) and 2 mM glutamine and incubated at 37° C.with 5% CO₂. Cells were grown to 40% confluency and quadruple wells weretreated as follows: (a) untreated cells as negative controls, (b) 10⁸non-targeted empty minicells, (c) 10⁸ targeted empty minicells, (d) 10⁸non-targeted Doxorubicin-packaged minicells, and (e) 10⁸ targetedDoxorubicin-packaged minicells. The incubation reaction was terminatedafter 8 hrs in 2 wells of each sample and the remaining duplicatesamples were terminated after 24 hrs. After incubation, the cells werewashed four times with PBS and fixed with 4% formaldehyde for 10 min.The fixative was washed three times with PBS and the coverslips wereinverted onto glass microscope slides with glycerol. The coverslips weresealed with 1% agarose.

The slides were viewed by fluorescence confocal microscopy (Fluoview,Olympus America, Melville, N.Y., USA). Fluorescence and DifferentialImage Contrast (DIC) images were collected and the results revealed thatwithin 8 hrs of incubation, targeted (carrying the Alexa Fluor488-conjugated bispecific antibody; green fluorescence)Doxorubicin-packaged minicells showed most cells covered by severalgreen fluorescent dots, while the non-targeted (lacking thefluorescence-labeled bispecific antibody) showed only some greenfluorescent dots on very few cells. This suggested that the bispecificantibody specifically enabled the Doxorubicin-packaged minicells tostrongly adhere to the surface of the astrocytoma cells, presumably viathe EGF receptor. After 24 hrs co-incubation of astrocytoma cells andDoxorubicin-packaged minicells (targeted and non-targeted), the results,when visualized for red fluorescence (Doxorubicin autofluorescence isred), showed that most astrocytoma cells carried intense red fluorescentdots on the cell surface and many cells showed diffuse red fluorescencewithin the cell cytoplasm, as determined by viewing sections through thecell by fluorescence confocal microscopy. This result contrasted withthat for astrocytoma cells incubated for 24 hrs with non-targetedDoxorubicin-packaged minicells, where only a few red fluorescent dots(non-specific adhesion of minicells) could be observed on a few cells.This suggests that many of the Doxorubicin-packaged minicells had beeninternalized, most likely via EGF receptor-mediated endocytosis and thatsome minicells had broken down and released the Doxorubicin within theastrocytoma cell cytoplasm. The results were further confirmed when thegreen fluorescent and red fluorescent images were merged to reveal thatmost of the green dots co-localized with the red dots, resulting inyellow dots. The diffuse red fluorescence observed earlier within theastrocytoma cell cytoplasm remained red, suggesting that the Doxorubicin(red autofluorescence) was no longer packaged within the minicells(revealed green by minicell surface localized bispecific antibody),further suggesting that some minicells that had been endocytosed hadbroken down and released the Doxorubicin within the astrocytoma cellcytoplasm.

EXAMPLE 6 Efficiency of Minicell-Mediated Drug Delivery toNon-Phagocytic Mammalian Cells

This example demonstrates the efficiency of minicell-mediated drugdelivery to non-phagocytic mammalian cells. A colorimetric cytotoxicityassay (Promega; CellTiter 96 Aqueous One™) was used. MDA-MB-468 humanbreast adenocarcinoma cells were treated with ^(EGFR)minicells_(DOX) orcontrols comprising free Doxorubicin and ^(non-targeted)minicells_(DOX).MDA-MB 468 cells were seeded at 5×10⁶ cells in T75 flasks and incubatedfor 48 hrs to obtain ˜1×10⁷ cells/flask. The media was changed and cellswere treated with 10^(9 non-targeted)minicells_(DOX) or^(EGFR)Minicells_(DOX). Free Doxorubicin (50 ng/ml) was also included asa positive control. The cells were incubated for 24 hrs, washedthoroughly with 3 changes of PBS and trypsinized. Viable cells werecounted in a haemocytometer using the trypan blue exclusion method.1×10⁴ cells/ml per well were aliqouted into 24-well plates (6 wells pertreatment) and incubated for 3, 4, 5, and 6 days with media changeseveryday. MTS assay was performed at each time point according to themanufacturers instructions. Briefly, 100 μL of MTS reagent was added toeach well and color development was monitored over 2.5 hrs to 4 hrs. 100μL from each well was transferred to a 96-well plate and the absorbancewas read at 490 nm.

The results showed (FIG. 2) that the cytotoxicity of^(EGFR)Minicells_(DOX) was similar to that of free Doxorubicin,suggesting that ^(EGFR)Minicells_(DOX) delivered Doxorubicin in itsactive form to the MDA cells and that the efficiency of drug deliverywas over 95%, ^(non-targeted)Minicells_(DOX) did not show any toxicityto the cancer cells, suggesting that the targeting mechanism wasimportant for safety of the minicell-based drug therapy, becausenon-phagocytic mammalian cells do not appear to non-specificallyendocytose the minicells.

EXAMPLE 7 Highly Efficient Delivery of Chemotherapeutic Drug DoxorubicinVia Targeted and Drug-Packaged Minicells to Human Breast CancerXenografts in Nude Mice

This example demonstrates that bispecific ligand-targeted andDoxorubicin-packaged intact minicells can effect regression of humanbreast cancer cell tumor xenografts established in 6 week old femaleathymic nude mice.

As described above, minicells were obtained from an S. typhimuriumminCDE-mutant strain and were purified using a gradientcentrifugation/filamentation/filtration/endotoxin removal procedure. Thepurified minicells were packaged with chemotherapeutic drug Doxorubicinas described in Example 1.

A bispecific antibody was constructed as described in Example 3. Ananti-EGFR monoclonal antibody was selected because the xenografted cellswere human breast cancer cells MDA-MB-468 that are known to overexpressthe EGF receptor on the cell surface.

Recombinant minicells (10¹⁰) were incubated with the proteinA/G-bispecific antibody for 1 hour at room temperature, to coat theminicells with the antibody via its anti-LPS Fab region.

The mice used in this example were purchased from Animal ResourcesCentre, Perth, Wash., Australia, and all animal experiments wereperformed in compliance with the guide of care and use of laboratoryanimals and with Animal Ethics Committee approval. The experiments wereperformed in the NSW Agriculture accredited small animal facility atEnGeneIC Pty Ltd (Sydney, NSW, Australia). Human breast adenocarcinomacells (MDA-MB-468, ATCC; human mammary epithelial cells; non-phagocytic)were grown in tissue culture to full confluency in T-75 flasks in RPMI1640 medium supplemented with 5% Bovine Calf Serum (GIBCO-BRL LifeTechnologies, Invitrogen Corporation, Carlsbad, Calif., USA) andglutamine (Invitrogen) in a humidified atmosphere of 95% air and 5% CO₂at 37° C. 1×10⁶ cells in 50 uL serum-free media together with 50 uLgrowth factor reduced matrigel (BD Biosciences, Franklin Lakes, N.J.,USA) were injected subcutaneously between the shoulder blades of eachmouse using a 23-gauge needle. The tumors were measured twice a weekusing an electronic digital caliper (Mitutoyo, Japan, precision to0.001) and mean tumor volume was calculated using the formula, length(mm)×width² (mm)×0.5=volume (mm³). 16 days post-implantation, the tumorsreached volumes between 50 mm³ and 80 mm³, and mice were randomized toseven different groups of 11 per group.

The experiment was designed as follows. Group 1 (control) received notreatment. Group 2 (control) received free Doxorubicin (5 μg/gm of mousebody weight) intratumorally. This control was included to determine theeffect of free Doxorubicin on tumor cells and to assess toxicside-effects. Group 3 (control) was the same as group 2, except that theDoxorubicin was administered intravenously. Group 4 (control) receivedthe anti-O antigen/anti-EGFR BsAb and free Doxorubicin intravenously toshow the effect of BsAb in the absence of minicells. Groups 5 and 6received ^(non-targeted)minicells_(DOX) intravenously andintratumorally, respectively, to determine if drug-packaged butnon-targeted minicells could effect tumor stabilization. Groups 7 and 8received EGFR-targeted ^(EGFR)Minicells_(DOX) intravenously andintratumorally, respectively, to determine if receptor-targeted,drug-packaged minicells could effect tumor stabilization. Group 8 wasincluded to determine if the targeted, Doxorubicin-packaged minicellsgiven in the tail vein could follow the required sequence of events toachieve tumor stabilization and/or regression: i.e., permeate the leakyvasculature at the tumor site (shoulder blade region), diffuse throughthe tumor microenvironment, specifically bind to the human breast cancercells, be endocytosed, broken down intracellularly and release the drugpayload in its bioactive form into the cancer cell cytoplasm to resultin cell death and hence either tumor stabilization and/or regression.Minicells were administered at a dose of 10⁸ and all treatments weregiven on days 17, 24, 27 and 56 post-xenograft establishment. Allmeasurements were performed by an investigator who was blinded to thetreatments administered. Statistical analysis was performed by analysisof variance (ANOVA) and P<0.05 was considered to be statisticallysignificant.

The results showed (FIG. 3) that highly significant (p=0.0004) tumorstabilization/regression was only observed with ^(EGFR)Minicells_(DOX)treatment, whether given intravenously or intratumorally. No tumorregression was observed with ^(non-targeted)minicells_(DOX), suggestingthat the BsAb-mediated targeting was essential. At day 63, the treatmentfor the minicells_(DOX) group was changed to ^(EGFR)Minicells_(DOX)treatment to determine if the large tumor volumes (800 mm³ to 1,200 mm³)could be regressed via the targeted therapy. The result was a dramatictumor regression; by day 79, with just two ^(EGFR)minicells_(DOX)treatments, the tumor volumes had regressed to between 100 mm³ and 150mm³. The complete experiment was performed 3 times, each time yieldingsimilar results. This showed that the BsAb-targeted minicells couldspecifically deliver a chemotherapeutic drug to a human tumor xenograftin-vivo.

The result is a first demonstration of targeted in-vivo drug delivery tonon-phagocytic mammalian cells mediated by bacterially derived intactdrug-packaged minicells.

Interestingly, the free Doxorubicin given in the tail vein of mice(Groups 3 and 4) showed severe reaction at the site of the injection, awell known side-effect of free Doxorubicin intravenous injections inhumans. This reaction, known as Phlebitis, is thought to be caused bydrug extravasation at the site of injection, and associated killing ofnormal cells in the localized region. In contrast, the mice giventargeted or non-targeted Doxorubicin-packaged minicells did not show anyadverse reaction at the site on the injection, suggesting that theminicell-packaged Doxorubicin prevented free Doxorubicin reactivity withskin tissue at the site of injection. Additionally, unlike liposomaldelivery vectors, e.g., DOXIL (liposomal doxorubicin), the drug did notleak from minicells.

These results suggest the following: (a) minicells are able to package apotentially highly toxic drug like Doxorubicin in the minicell cytoplasmand the drug does not appear to leak out of the minicell membrane.Hence, the lack of skin reactivity to at the site of the tail veininjection (Groups 5 and 7) that was seen with free Doxorubicin (Groups 3and 4), (b) Doxorubicin-packaged minicells are safe to at least the nudemice when the minicells are injected intravenously or intratumoraly(Groups 5 to 8), suggesting that the free endotoxin (lipopolysaccharide)removal procedure adopted and previously invented by the currentinventors (U.S. patent application number PCT/IB02/04632) is sufficientto provide a dose of minicells sufficiently free of endotoxin to be safefor intravenous or intratumoral subcutaneous administration, (c)targeted minicells appear to be small enough to permeate the leaky tumorneovasculature, to enable Doxorubicin-packaged minicells to enter intothe tumor microenvironment, (d) targeted Doxorubicin-packaged minicellsappear to specifically bind to the EGF receptor that is known to beoverexpressed on the surface of MDA-MB-468 cells and post-endocytosis,the minicells break down and release Doxorubicin, resulting in tumorcell death and the observed tumor regression (Group 7; FIG. 3), (e)following intravenous injection the targeted and Doxorubicin-packagedminicells reach the tumor microenvironment in significant concentrationto achieve tumor regression. Accordingly, minicells do not appear tohave been eliminated by circulating professional phagocytic cells insignificant quantities to obviate the observed therapeutic effect.

EXAMPLE 8 Highly Efficient Delivery of Hydrophobic Chemotherapeutic DrugPaclitaxel Via Targeted and Drug-Packaged Minicells to Human BreastCancer Xenografts in Nude Mice

This example demonstrates highly efficient delivery of a hydrophobicchemotherapeutic drug, Paclitaxel, to human breast cancer xenografts innude mice via targeted and drug-packaged minicells. The experiment shownin example 7 was repeated using ^(EGFR)Minicells_(Paclitaxel) as theexperimental treatment. The treatments included, (i) G1—tumor only, (ii)G2—free Paclitaxel (400 μg) given intratumorally, (iii) G3—FreePaclitaxel (400 μg) given intravenously, (iv) G4—anti-Oantigen/anti-EGFR BsAb and free Paclitaxel (400 μg) given intravenously,(v) G5—^(non-targeted)minicells_(Pac) given intravenously, (vi)G6—^(non-targeted)minicells_(Pac) given intratumorally, (vii)G7—^(EGFR)minicells_(Pac) given intravenously, (viii)G8—^(EGFR)minicells_(Pac) given intratumorally. The various treatmentswere given on days 15, 21, 26, 29 and 33. 1×10⁸ minicells were used ineach minicell treatment.

The results showed (FIG. 4) highly significant (p=0.0004) tumorstabilization/regression in mice treated with ^(EGFR)minicells_(Pac)and, once more, it did not matter whether the treatment was givenintravenously or intratumorally. The control treatments including^(non-targeted)minicells_(Pac), BsAb and free paclitaxel had anegligible effect on tumor growth. Throughout the experiment, mice didnot show any overt signs of toxicity such as fever, lethargy, loss ofappetite or death. The experiment was repeated 3 times with similarresults.

This result is particularly significant, because other drug deliveryvectors, like liposomes, nanoparticles, etc., have not successfullypackaged therapeutically significant amounts of highly hydrophobic drugslike Paclitaxel. In most cases, attempts were made to change thechemical structure of the vector or the drug to enable drug packaging,often resulting in loss of bioactivity. Our result is the first showingthat not only can such drugs be readily packaged in intact minicells,but they can be safely delivered specifically to target diseased cellsin-vivo to achieve a therapeutic effect.

EXAMPLE 9 Demonstration of Versatility of Targeted Minicell-Based DrugDelivery to Mammalian Cells

This example demonstrates the following: (i) targeted, drug-packagedminicell vectors are versatile enough to achieve a therapeutic effect ina range of different non-phagocytic cells, (ii) the targeting mechanismis versatile enough to enable the use of different cell-surface receptortargets on diseased cells and is not restricted to the EGF receptor, and(iii) the minicell vector itself is versatile enough to enable the useof minicells derived from different bacterial genera.

In a single nude mouse xenograft experiment, (i) human ovarian cancercells (SKOV3; ATCC. USA) were used to establish the tumor xenograft,(ii) the targeting BsAb was constructed using anti-O antigen MAb andanti-HER2/neu MAb (The latter receptor is known to be overexpressed onthe surface of SKOV3 cells), and (iii) minicells used for the treatmentwere derived both from S. Typhimurium and E. coli minCDE-strains. Theminicells were packaged with Doxorubicin.^(non-targeted)minicells_(DOX), BsAb (anti-HER2/anti-O antigen) and freeDoxorubicin were included as controls.

The results showed (FIG. 5) significant tumor stabilization in micetreated with either S. Typhimurium minCDE- or E. coli minCDE-derived^(HER2)minicells_(DOX) (p=0.004). The SKOV3 xenografts grew much morerapidly than MDA-MB-468 xenografts, and the experiment could only befollowed up to 31 days post-xenograft establishment because the controlanimals had reached the point of death or euthanasia.

These results demonstrated (i) that intact minicells can be used todeliver drugs in-vivo to a range of different non-phagocytic mammaliancells, (ii) that intact minicell vectors can be targeted to a diverserange of cell surface receptors found on the diseased cells, and (iii)that minicells can be derived from different bacterial genera orspecies, yet function in a similar way, particularly with respect todrug delivery to target cells in-vivo.

EXAMPLE 10 The Relationship Between Targeted, Drug-Packaged MinicellDose and Therapeutic Effect on Human Tumor Xenografts in Nude Mice

This example demonstrates the dose-effect relationship for drug-packagedminicells. More specifically, the example shows the dose of targeted,drug-packaged minicells required to achieve maximal therapeutic effecton human tumor xenografts in nude mice.

MDA-MB-468 (human breast adenocarcinoma) cells were established asxenografts between the shoulder blades of Balb/c nu/nu mice. S.Typhimurium minCDE-derived minicells were packaged with Doxorubicinusing two different external Doxorubicin concentrations, 60 μg/ml and200 μg/ml as described in example 3. The minicells_(DOX) were purified(example 1) and samples were analyzed by HPLC to determine theconcentration of Doxorubicin packaged within 10⁸ minicells. The resultsshowed that at external Doxorubicin concentrations of 60 μg/ml and 200μg/ml, 10⁸ minicells packaged 85 ng and 660 ng of Doxorubicin,respectively.

The minicells_(DOX) were then targeted to the EGFR that is overexpressedon MDA-MB-468 cells and six different mouse intravenous doses wereprepared, (i) G1—10^(8 EGFR)minicells_(DOX) carrying a total of 660 ngDoxorubicin, (ii) G2—10^(8 EGFR)minicells_(DOX) carrying a total of 85ng Doxorubicin, (iii) G3—10^(7 EGFR)minicells_(DOX) carrying a total of66 ng Doxorubicin, (iv) G4—10^(7 EGFR)minicells_(DOX) carrying a totalof 8.5 ng Doxorubicin, (v) G5—10^(6 EGFR)minicells_(DOX) carrying atotal of 6.6 ng Doxorubicin, and (vi) G6—10^(6 EGFR)minicells_(DOX)carrying a total of 0.85 ng Doxorubicin. Post-xenograft establishmentwith tumor volumes between 50 mm³ to 80 mm³, the various doses wereintravenously administered to the mice. Tumor volumes were measured aspreviously described.

The results showed (FIG. 6) a clear relationship between minicell doseand the therapeutic effect. In terms of tumor stabilization/regression,10^(8 EGFR)minicells_(DOX) were more effective than10^(7 EGFR)minicells_(DOX), which in turn were more effective than10^(6 EGFR)minicells_(DOX). Interestingly, there was no major differencein the Doxorubicin concentration between minicells administered togroups 3 and 4 (6.6 ng and 8.5 ng respectively) and groups 5 and 6 (66ng and 85 ng). However, the treatment in G4 was more effective than G3and, similarly, treatment in G6 was more effective than G5. Thissuggested that within the range of minicell and drug concentrationsanalyzed in this experiment, the therapeutic effect correlated tominicell numbers rather than to the concentration of drug carried withinthe minicells.

CITED PUBLICATIONS

This application incorporates by reference each of the followingpublications:

-   Alberts et al., Intraperitoneal cisplatin plus intravenous    cyclophosphamide versus intravenous cisplatin plus intravenous    cyclophosphamide for Stage III ovarian cancer, N. Engl. J. Med.,    335: 1950-1955 (1996).-   Allen et al., Chronic liposome administration in mice: effects on    reticuloendothelial function and tissue distribution, J. Pharmacol.    Exp. Therap., 229: 267-275 (1984).-   Allen T M, Liposomes: opportunities in drug delivery, Drugs, 54    Suppl 4: 8-14 (1997).-   Alkan-Onyuksel et al., A mixed micellar formulation suitable for the    parenteral administration of taxol, Pharm. Res., 11(2): 206-12    (1994).-   Arndt et al., Alkylphospholipid liposomes: preparation, properties    and use in cancer research, Drugs of Today, 34 (Suppl. F): 83-96    (1998).-   Barenholz, Liposome application: problems and prospects, Curr. Opin.    Colloid Interface. Sci., 6: 66-77 (2001).-   Batra et al., Receptor-mediated gene delivery employing    lectin-binding specificity, Gene Ther., 1(4): 255-60 (1994).-   Becker et al., Gene therapy of prostate cancer with the soluble    vascular endothelial growth factor receptor Flk1, Cancer Biol.    Ther., 1(5):548-53 (2002).-   Borges-Walmsley & Walmsley, The structure and function of drug    pumps, Trends Microbiol. 9: 71-79 (2001).-   Britton et al., “Characterization of a prokaryotic SMC protein    involved in chromosome partitioning,” Genes Dev., 12: 1254 (1998).-   Carter, Improving the efficacy of antibody-based cancer therapies,    Nat. Rev. Cancer, 1(2): 118-29 (2001).-   Chan et al., Prospective randomized trial of docetaxel versus    Doxorubicin in patients with metastatic breast cancer, J. Clin.    Oncol., 17:2341-54 (1999).-   Chonn & Cullis, Recent advances in liposomal drug-delivery systems,    Curr. opinion in Biotechnology, 6(6): 698-708 (1995).-   Cowan et al., Randomized trial of Doxorubicin, bisantrene, and    mitoxantrone in advanced breast cancer, J. Natl. Cancer Inst., 83:    1077-84 (1991).-   Cullis et al., Influence of pH gradients on the transbilayer    transport of drugs, lipids, peptides and metal ions into large    unilamellar vesicles, Biochim. Biophys. Acta, 1331: 187-211 (1997).-   Daemen et al., Liposomal Doxorubicin-induced toxicity: depletion and    impairment of phagocytic activity of liver macrophages, Int. J.    Cancer, 61: 716-721 (1995).-   Daemen et al., Toxicity of Doxorubicin entrapped within    long-circulating liposomes, J. Controlled Release, 44: 1-9 (1997).-   de Haard et al., A large non-immunized human Fab fragment phage    library that permits rapid isolation and kinetic analysis of high    affinity antibodies, J. Biol. Chem., 274: 18218-18230 (1999).-   DeMario M D and Ratain M I. Oral chemotherapy: rationale and future    directions, J. Clin. Oncol., 16(7): 2557-2567 (1998).-   Dubel et al., Bifunctional and multimeric complexes of streptavidin    fused to single chain antibodies (scFv), J. Immunol. Methods, 178:    201-209 (1995).-   Gabizon et al., Pharmacokinetics of pegylated liposomal Doxorubicin:    review of animal and human studies, Clin. Pharmacokinet., 42: 419-36    (2003).-   Glennie et al., Preparation and performance of bispecific F(ab′    gamma)2 antibody containing thioether-linked Fab′ gamma    fragments, J. Immunol., 139(7): 2367-75 (1987).-   Gosselin & Lee, Folate receptor-targeted liposomes as vectors for    therapeutic agents, Biotechnol. Annu. Rev., 8: 103-31 (2002).-   Gregoriadis, Targeting of drugs: implications in medicine, Lancet,    II: 241-6 (1981).-   Griffiths et al., Isolation of high affinity human antibodies    directly from large synthetic repertoires, EMBO J., 13: 3245-3260    (1994).-   Harry, “Bacterial cell division: Regulating Z-ring formation,” Mol.    Microbiol., 40: 795 (2001).-   Heim et al., “Wavelength mutations and posttranslational    autoxidation of green fluorescent protein,” Proc. Nat'l. Acad. Sci.    USA, 91: 12501 (1994).-   Henderson et al., Randomized clinical trial comparing mitoxantrone    with Doxorubicin in previously treated patients with metastatic    breast cancer, J. Clin. Oncol., 7: 560-71 (1989).-   Hiraga et al., “Chromosome partitioning in Escherichia coli: novel    mutants producing anucleate cells,” J. Bacteriol., 171: 1496 (1989).-   Hoshida et al., Gene therapy for pancreatic cancer using an    adenovirus vector encoding soluble flt-1 vascular endothelial growth    factor receptor, Pancreas, 25(2): 111-21 (2002).-   Hu et al., Minibody: A novel engineered anti-carcinoembryonic    antigen antibody fragment (single-chain Fv-CH3) which exhibits    rapid, high-level targeting of xenografts, Cancer Res., 56:    3055-3061 (1996).-   Hu & Lutkenhaus, “Topological regulation of cell division in    Escherichia coli involves rapid pole to pole oscillation of the    division inhibitor MinC under the control of MinD and MinE,” Mol.    Microbiol., 34: 82 (1999).-   Hudson & Souriau, Recombinant antibodies for cancer diagnosis and    therapy, Expert Opin. Biol. Ther., 1: 845-855 (2001).-   Hudson & Souriau, Engineered antibodies, Nat. Med., 9(1): 129-34    (2003).-   Hung et al., Development of clinical trial of E1A gene therapy    targeting HER-2/neu-overexpressing breast and ovarian cancer, Adv.    Exp. Med. Biol., 465: 171-80 (2000).-   Ireton et al., spo0J is required for normal chromosome segregation    as well as the initiation of sporulation in Bacillus subtilis, J.    Bacteria., 176: 5320 (1994).-   Janoff, A., ed., Liposomes, Rational Design. New York: Marcel Dekker    (1998).-   Jones et al., Replacing the complementarity-determining regions in a    human antibody with those from a mouse, Nature, 321: 522-525 (1986).-   Kaetzel et al., The polymeric immunoglobulin receptor: structure and    synthesis, Biochem. Soc. Trans., 25: 475-480 (1997).-   Karpovsky et al., Production of target-specific effector cells using    hetero-cross-linked aggregates containing anti-target cell and    anti-Fc gamma receptor antibodies, J. Exp. Med., 160(6): 1686-701    (1984).-   Kemp et al., Amifostine pretreatment for protection against    cyclophosphamide induced and cisplatin-induced toxicities: results    of a randomized control trial in patients with advanced ovarian    cancer, J. Clin. Oncol., 14: 2101-2112 (1996).-   Kerem et al., “Identification of the cystic fibrosis gene: genetic    analysis,” Science, 245: 1073 (1989).-   Kirmani et al., A comparison of intravenous versus intraperitoneal    chemotherapy for the initial treatment of ovarian cancer, Gynecol.    Oncol., 54(3): 338-344 (1994).-   Kleeff et al., Targeting of suicide gene delivery in pancreatic    cancer cells via FGF receptors, Cancer Gene Ther., 9(6): 522-32    (2002).-   Knappik et al., Fully synthetic human combinatorial antibody    libraries (HuCAL) based on modular consensus frameworks and CDRs    randomized with trinucleotides, J. Mol. Biol., 296: 57-86 (2000).-   Kostelny et al., Formation of a bispecific antibody by the use of    leucine zippers, J. Immunol., 148(5): 1547-53 (1992).-   Kumanohoso et al., Enhancement of therapeutic efficacy of bleomycin    by incorporation into biodegradable poly-d,I-lactic acid, Cancer    Chemother. Pharmacol., 40: 112-116 (1997).-   Lasic & Martin, editors, Stealth liposomes. Boca Raton: CRC Press    (1995).-   Lasic & Papahadjopoulos, editors, Medical Applications of Liposomes.    New York: Elsevier (1998).-   Levin et al., “Identification of Bacillus subtilis genes for septum    placement and shape determination,” J. Bacteriol., 174: 6717 (1992).-   Mekhail & Markman, Paclitaxel in cancer therapy, Expert Opin.    Pharmacother., 3: 755-766 (2002).-   Norris et al., Phase III comparative study of vinorelbine combined    with Doxorubicin versus Doxorubicin alone in disseminated    metastatic/recurrent breast cancer, J. Clin. Oncol., 18: 2385-94    (2000).-   Okada et al., “Possible function of the cytoplasmic axial filaments    in chromosomal segregation and cellular division of Escherichia    coli,” Sci. Prog., 77: 253 (1993-94).-   Okada et al., “Cytoplasmic axial filaments in Escherichia coli    cells: possible function in the mechanism of chromosome segregation    and cell division,” J. Bacteriol., 176: 917 (1994).-   Osbourn et al., Current methods for the generation of human    antibodies for the treatment of autoimmune diseases, Drug Delivery    Tech., 8: 845-851 (2003).-   Pack & Pluckthun, Miniantibodies: use of amphipathic helices to    produce functional, flexibly linked dimeric Fv fragments with high    avidity in Escherichia coli, Biochemistry, 31(6): 1579-84 (1992).-   Paridaens et al., Paclitaxel versus Doxorubicin as first-line    single-agent chemotherapy for metastatic breast cancer, J. Clin.    Oncol., 18: 724-33 (2002).-   Pikaar et al., “Opsonic activities of surfactant proteins A and D in    phagocytosis of gram-negative bacteria by alveolar macrophages,” J.    Infect. Dis., 172: 481 (1995).-   Prasher et al., “Using GFP to see the light,” Trends in Genetics,    11: 320 (1995).-   Puisieux et al., editors, Liposomes, New Systems and New Trends in    Their Applications. Paris: Editions de Sant'e (1995)-   Raskin & de Boer, “MinDE-dependent pole-to-pole oscillation of    division inhibitor MinC in Escherichia coli,” J. Bacteria, 181: 6419    (1999).-   Reeve, “Use of minicells for bacteriophage-directed polypeptide    synthesis,” Methods Enzymol., 68: 493 (1979).-   Ridgway et al., ‘Knobs-into-holes’ engineering of antibody CH3    domains for heavy chain heterodimerization, Protein Eng., 9(7):    617-21 (1996).-   Riechmann et al., Reshaping human antibodies for therapy, Nature,    332: 323-327 (1988).-   Riezman, “Three clathrin-dependent budding steps and cell polarity,”    Trends in Cell Biology., 3: 330 (1993).-   Riordan et al., “Identification of the cystic fibrosis gene: cloning    and characterization of complementary DNA,” Science, 245: 1066    (1989).-   Rommens et al., “Identification of the cystic fibrosis gene:    Chromosome walking and jumping,” Science, 245: 1059 (1989).-   Salomon et al., Epidermal growth factor-related peptides and their    receptors in human malignancies, Crit. Rev. Oncol. Hematol., 19:    183-232 (1995).-   Sandvig & Deurs, “Endocytosis without clathrin,” Trends in Cell    Biology, 4: 275 (1994).-   Sarosy & Reed, Taxol dose intensification and its clinical    implications, J. Natl. Med. Assoc., 85(6): 427-31 (1993).-   Schiller et al., Amifostine, Cisplatin, and Vinblastine in    metastatic non-small cell lung cancer: a report of high response    rates and prolonged survival, J. Clin. Oncol., 14: 1913-1921 (1996).-   Shangara et al., “Suicide genes: past, present and future    perspectives,” Immunology Today, 21: 48 (2000).-   Shapiro et al., A randomized comparison of intra-arterial versus    intravenous BCNU, with or without intravenous 5-fluorouracil, for    newly diagnosed patients with malignant glioma, J. Neurosurg., 76:    772-781 (1992).-   Sharma et al., Novel Taxol formulation: polyvinylpyrrolidone    nanoparticle encapsulated Taxol for drug delivery in cancer therapy,    Oncology Res., 8(8-9): 281-286 (1996).-   Sheets et al., Efficient construction of a large nonimmune phage    antibody library: the production of high-affinity human single-chain    antibodies to protein antigens, Proc. Natl. Acad. Sci. USA, 95:    6157-6162 (1998).-   Sipos et al., Optimizing interstitial delivery of BCNU from    controlled release polymers for the treatment of brain tumors,    Cancer Chemother. Pharmacol., 39: 383-389 (1997).-   Slepushkin et al., Sterically stabilized pH-sensitive liposomes.    Intracellular delivery of aqueous contents and prolonged circulation    in vivo, J. Biological Chem., 272(4): 2382-2388 (1997).-   Speert et al., “Functional characterization of macrophage receptors    for In-vitro phagocytosis of unopsonized pseudomonas-aeruginosa,” J.    Clin. Invest., 82: 872 (1988).-   Spencer, “Developments in suicide genes for preclinical and clinical    applications,” Molecular Therapeutics, 2: 433 (2000).-   Stewart & D'Ari, “Genetic and morphological characterization of an    Escherichia coli chromosome segregation mutant,” J. Bacteriol., 174:    4513 (1992).-   Thurnher et al., Carbohydrate receptor-mediated gene transfer to    human T leukaemic cells, Glycobiology, 4(4): 429-35 (1994).-   Todorovska et al., Design and application of diabodies, triabodies    and tetrabodies for cancer targeting, J. Immunol. Methods, 248:    47-66 (2001).-   Tomlinson & Holliger, Methods for generating multivalent and    bispecific antibody fragments, Methods Enzymol., 326: 461-479    (2000).-   Vaughan et al., Human antibodies with subnanomolar affinities    isolated from a large non-immunized phage display library, Nature    Biotechnol., 14: 309-314 (1996).-   Vaughan et al., Human antibodies by design, Nature Biotechnol., 16:    535-539 (1998).-   Verhoeyen et al., Reshaping human antibodies: grafting an    antilysozyme activity, Science, 239: 1534-1536 (1988).-   Wachi et al., “New mre genes mreC and mreD, responsible for    formation of the rod shape of Escherichia coli cells,” J.    Bacteriol., 171: 6511 (1989).-   White, Liposomal daunorubicin is not recommended in patients with    less than advanced HIV related Kaposi's sarcoma, Aids, 11: 1412-1413    (1997).-   Woodle & Lasic, Sterically stabilized liposomes, Biochim. Biophys.    Acta, 1113: 171-99 (1992).-   Wright & Jong, “Interferon-gama depresses binding of ligand by c3b    and c3bi receptors on cultured human monocytes, an effect reversed    by fibronectin,” Experimental Medi., 163: 1245 (1986).-   Yazawa et al., “Current progress in suicide gene therapy for    cancer,” World J. Surg., 26: 783 (2002).-   Ziady et al., Gene transfer into hepatoma cell lines via the serpin    enzyme complex receptor, Am. J. Physiol., 273(2 Pt 1): G545-52    (1997).

What is claimed is:
 1. A composition comprising (i) at least 10⁷ intactbacterial minicell, which are approximately 400 nm in diameter, (ii) abispecific antibody having specificity for a cancer cell surfacereceptor and specificity for said minicell, wherein said bispecificantibody is attached to said minicell, and (iii) a pharmaceuticalacceptable carrier, wherein said composition is free of membrane blebsof 200 nm or less in size, and wherein said composition contains fewerthan about 1 contaminating parent bacterial cell per 10⁹ minicells. 2.The composition of claim 1, wherein said composition contains fewer thanabout 1 contaminating parent bacterial cell per 10¹⁰ minicells.
 3. Thecomposition of claim 1, wherein said composition contains fewer thanabout 1 contaminating parent bacterial cell per 10¹¹ minicells.
 4. Thecomposition of claim 1, wherein the cancer cell surface receptor isselected from the group consisting of carcinoembryonic antigen (CEA),heregulin receptors HER-2, neu, and c-erbB-2, epidermal growth factorreceptor (EGFR), asialoglycoprotein receptor, transferrin receptor,serpin enzyme complex receptor, fibroblast growth factor receptor(FGFR), vascular endothelial growth factor receptor (VEGFR), folatereceptor, cell surface glycocalyx, carbohydrate receptor and polymericimmunoglobulin receptor.
 5. The composition of claim 1, wherein theminicells are derived from Salmonella typhimurium.
 6. A compositioncomprising (i) at least 10⁷ intact bacterial minicells, which areapproximately 400 nm in diameter and loaded with a therapeuticallyeffective amount of a chemotherapeutic drug, (ii) a bispecific antibodyhaving specificity for a cancer cell surface receptor and specificityfor said minicell, wherein said bispecific antibody is attached to saidminicell, and (iii) a pharmaceutical acceptable carrier, wherein saidcomposition is free of membrane blebs of 200 nm or less in size, whereinsaid composition contains fewer than about 1 contaminating parentbacterial cell per 10⁹ minicells.
 7. The composition of claim 6, whereinsaid composition contains fewer than about 1 contaminating parentbacterial cell per 10¹⁰ minicells.
 8. The composition of claim 6,wherein the cancer cell surface receptor is selected from the groupconsisting of carcinoembryonic antigen (CEA), heregulin receptors HER-2,neu, and c-erbB-2, epidermal growth factor receptor (EGFR),asialoglycoprotein receptor, transferrin receptor, serpin enzyme complexreceptor, fibroblast growth factor receptor (FGFR), vascular endothelialgrowth factor receptor (VEGFR), folate receptor, cell surfaceglycocalyx, carbohydrate receptor and polymeric immunoglobulin receptor.9. The composition of claim 8, wherein the minicells are derived fromSalmonella typhimurium.
 10. The composition of claim 6, wherein thechemotherapeutic drug is doxorubicin, vinblastine or paclitaxel.
 11. Thecomposition of claim 10, wherein the minicells are loaded with at least8.5 ng of doxorubicin.
 12. The composition of claim 11, wherein each ofthe minicells is loaded with at least 8.5×10⁻⁷ ng of doxorubicin.